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Metabolic Fate (metabolic + fate)

Distribution by Scientific Domains

Life Sciences	50%
Chemistry	35%
Medical Sciences	14%

Selected Abstracts

Metabolic fate of l -lactaldehyde derived from an alternative l -rhamnose pathway

FEBS JOURNAL, Issue 20 2008
Seiya Watanabe
Fungal Pichia stipitis and bacterial Azotobacter vinelandii possess an alternative pathway of l -rhamnose metabolism, which is different from the known bacterial pathway. In a previous study (Watanabe S, Saimura M & Makino K (2008) Eukaryotic and bacterial gene clusters related to an alternative pathway of non-phosphorylated l -rhamnose metabolism. J Biol Chem283, 20372,20382), we identified and characterized the gene clusters encoding the four metabolic enzymes [l -rhamnose 1-dehydrogenase (LRA1), l -rhamnono-,-lactonase (LRA2), l -rhamnonate dehydratase (LRA3) and l -2-keto-3-deoxyrhamnonate aldolase (LRA4)]. In the known and alternative l -rhamnose pathways, l -lactaldehyde is commonly produced from l -2-keto-3-deoxyrhamnonate and l -rhamnulose 1-phosphate by each specific aldolase, respectively. To estimate the metabolic fate of l -lactaldehyde in fungi, we purified l -lactaldehyde dehydrogenase (LADH) from P. stipitis cells l -rhamnose-grown to homogeneity, and identified the gene encoding this enzyme (PsLADH) by matrix-assisted laser desorption ionization-quadruple ion trap-time of flight mass spectrometry. In contrast, LADH of A. vinelandii (AvLADH) was clustered with the LRA1,4 gene on the genome. Physiological characterization using recombinant enzymes revealed that, of the tested aldehyde substrates, l -lactaldehyde is the best substrate for both PsLADH and AvLADH, and that PsLADH shows broad substrate specificity and relaxed coenzyme specificity compared with AvLADH. In the phylogenetic tree of the aldehyde dehydrogenase superfamily, PsLADH is poorly related to the known bacterial LADHs, including that of Escherichia coli (EcLADH). However, despite its involvement in different l -rhamnose metabolism, AvLADH belongs to the same subfamily as EcLADH. This suggests that the substrate specificities for l -lactaldehyde between fungal and bacterial LADHs have been acquired independently. [source]

Myocardial metabolism of triacylglycerol-rich lipoproteins in type 2 diabetes

THE JOURNAL OF PHYSIOLOGY, Issue 13 2009
You-Guo Niu
Cardiac utilisation of very-low-density lipoprotein (VLDL) and chylomicrons (CM) was investigated in the ZDF rat model of type 2 diabetes, in order to define the role of triacylglycerol (TAG) metabolism in the development of contractile dysfunction. Hearts from obese diabetic and lean littermate control rats were perfused with VLDL and CM from diabetic and control rats. Metabolic fate of the lipoprotein TAG and contractile function were examined. Myocardial utilisation of both VLDL- and CM-TAG was increased in the diabetic state. Diabetic hearts oxidised diabetic lipoprotein-TAG to a greater extent than control lipoproteins; glucose oxidation was decreased. There was no difference in lipoprotein-TAG assimilation into diabetic heart lipids; diabetic lipoproteins were, however, a poor substrate for control heart tissue lipid accumulation. Although the proportion of exogenous lipid incorporated into tissue TAG was increased in diabetic hearts perfused with control lipoproteins, this effect was not seen in diabetic hearts perfused with diabetic lipoproteins. Myocardial heparin-releasable lipoprotein lipase (LPL) activity was moderately increased in the diabetic state, and diabetic lipoproteins increased tissue-residual LPL activity. Cardiac hydraulic work was decreased only in diabetic hearts perfused with diabetic CM. Compositional analysis of diabetic variant lipoproteins indicated changes in size and apoprotein content. Alterations in cardiac TAG-rich lipoprotein metabolism in type 2 diabetes are due to changes in both the diabetic myocardium and the diabetic lipoprotein particle; decreased contractile function is not related to cardiac lipid accumulation from TAG-rich lipoproteins but may be associated with changes in TAG-fatty acid oxidation. [source]

Metabolic fate of l -lactaldehyde derived from an alternative l -rhamnose pathway

Proteolytic activation of internalized cholera toxin within hepatic endosomes by cathepsin D

FEBS JOURNAL, Issue 17 2005
Clémence Merlen
We have defined the in vivo and in vitro metabolic fate of internalized cholera toxin (CT) in the endosomal apparatus of rat liver. In vivo, CT was internalized and accumulated in endosomes where it underwent degradation in a pH-dependent manner. In vitro proteolysis of CT using an endosomal lysate required an acidic pH and was sensitive to pepstatin A, an inhibitor of aspartic acid proteases. By nondenaturating immunoprecipitation, the acidic CT-degrading activity was attributed to the luminal form of endosomal cathepsin D. The rate of toxin hydrolysis using an endosomal lysate or pure cathepsin D was found to be high for native CT and free CT-B subunit, and low for free CT-A subunit. On the basis of IC50 values, competition studies revealed that CT-A and CT-B subunits share a common binding site on the cathepsin D enzyme, with native CT and free CT-B subunit displaying the highest affinity for the protease. By immunofluorescence, partial colocalization of internalized CT with cathepsin D was confirmed at early times of endocytosis in both hepatoma HepG2 and intestinal Caco-2 cells. Hydrolysates of CT generated at low pH by bovine cathepsin D displayed ADP-ribosyltransferase activity towards exogenous Gs, protein suggesting that CT cytotoxicity, at least in part, may be related to proteolytic events within endocytic vesicles. Together, these data identify the endocytic apparatus as a critical subcellular site for the accumulation and proteolytic degradation of endocytosed CT, and define endosomal cathepsin D an enzyme potentially responsible for CT cytotoxic activation. [source]

Cultured Granule Cells and Astrocytes from Cerebellum Differ in Metabolizing Sphingosine

JOURNAL OF NEUROCHEMISTRY, Issue 2 2000
Laura Riboni
Sphingosine metabolism was studied in primary cultures of differentiated cerebellar granule cells and astrocytes. After a 2-h pulse with [C3 - 3H]sphingosine at different doses (0.1-200 nmol/mg of cell protein), both cell types efficiently incorporated the long chain base ; the percentage of cellular [3H]sphingosine over total label incorporation was extremely low at sphingosine doses of <10 nmol/mg of cell protein and increased at higher doses. Most of the [3H]sphingosine taken up underwent metabolic processing by N -acylation, 1-phosphorylation, and degradation (assessed as 3H2O released in the medium). The metabolic processing of exogenous sphingosine was extremely efficient in both cells, granule cells and astrocytes being able to metabolize, respectively, an amount of sphingosine up to 80- and 300-fold the cellular content of this long chain base in 2 h. At the different doses, the prevailing metabolic route of sphingosine was different. At lower doses and in a wide dose range, the major metabolic fate of sphingosine was N -acylation. With increasing doses, there was first increased sphingosine degradation and then increased levels of sphingosine-1-phosphate. The data demonstrate that, in neurons and astrocytes, the metabolic machinery devoted to sphingosine processing is different, astrocytes possessing an overall higher capacity to synthesize the bioactive compounds ceramide and sphingosine-1-phosphate. [source]

Impaired bioavailability of vitamin A in adults and children with persistent diarrhoea in Zambia

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 7 2001
P. Kelly
Background: We have previously demonstrated a strong relationship between low serum retinol concentration and mortality in Zambian AIDS patients with diarrhoea, but were unable to detect any benefit from oral micronutrient supplementation. Aim: To test the hypothesis that this is related to impaired availability of vitamin A, we analysed serum retinol concentration changes over 6 h following oral mega-dose therapy (60, 120 or 180 mg retinol). Methods: Twenty-four men without diarrhoea, 15 adults with persistent diarrhoea and 11 children (six girls, five boys) with persistent diarrhoea were studied. Results: Men with persistent diarrhoea had lower baseline serum retinol concentrations (median 0.39 ,mol/L, interquartile range 0.21,0.56) than controls (median 1.16 ,mol/L, interquartile range 0.84,1.47; P=0.0003). After 60 mg retinol, the rise in serum retinol in HIV seropositive controls (median 0.63 ,mol/L, interquartile range 0.35,0.77) did not differ significantly from that observed in HIV seronegative controls (median 0.35 ,mol/L, interquartile range , 0.04,0.56; P=0.20). Increasing the dose to 120 mg or 180 mg retinol did not enhance the increase in serum retinol concentration. The increase in serum retinol was less in adults with persistent diarrhoea (median 0.25 ,mol/L, interquartile range 0.04,0.35) and in children (median 0.11 ,mol/L, interquartile range 0.04,0.46) than in men without diarrhoea (median 0.44 ,mol/L, interquartile range 0.26,0.74; P=0.03). Adults and children with diarrhoea had greater losses of retinol in urine over a 24-h period than controls, but less than 1% of the ingested dose was excreted. Conclusions: These results suggest that persistent diarrhoea in this population is associated with reduced bioavailability of retinol. Further work is required to determine the metabolic fate of therapeutic doses of retinol and to determine appropriate replacement strategies for HIV infected individuals. [source]

Positive regulation of Bacillus subtilis ackA by CodY and CcpA: establishing a potential hierarchy in carbon flow

MOLECULAR MICROBIOLOGY, Issue 3 2006
Robert P. Shivers
Summary Conversion of pyruvate to acetate via the phosphotransacetylase-acetate kinase pathway generates ATP and is a major overflow pathway under conditions of carbon and nitrogen excess. In Bacillus subtilis, this pathway is positively regulated by CcpA, a global regulator of carbon metabolism genes. Transcription of the acetate kinase gene (ackA) proved to be activated as well by a second global regulatory protein, CodY. Expression of an ackA,lacZ fusion was reduced in a codY mutant strain. CodY was found to bind in vitro to two sites in the ackA promoter region and to stimulate ackA transcription in a run-off transcription assay. This is the first known case of direct positive regulation by CodY. CodY and CcpA were found to bind to neighbouring sites and their effects were additive both in vivo and in vitro. Surprisingly, positive regulation by CodY, unlike repression, responded primarily to only one type of effector molecule. That is, branched-chain amino acids (BCAAs) served as more potent co-activators of CodY-dependent ackA transcription than did GTP. Given the roles of CcpA and CodY in regulating genes whose products determine the metabolic fate of pyruvate, these two proteins may act together to mediate a hierarchical conversion of pyruvate to its many potential products. [source]

Selective bio-availability of phenolic acids from Scottish strawberries

MOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue S1 2009
Wendy R. Russell
Abstract Scottish strawberries were found to be a rich source of phenolic acids, namely benzoic (1287.95 ± 279.98 mg/kg) and cinnamic (1159.40 ± 233.96 mg/kg) acids, both free and attached to other plant components. Studies suggest a chemopreventative role for such compounds in several major clinical conditions, but the anticipated benefits are likely to be affected by their bio-availability and metabolic fate. In this pilot study, strawberries (750 g) was consumed by four healthy human volunteers (32 ± 6 years). Only the benzoic acids were detected in the plasma. Of these, the major free (gentisic, protocatechuic and p -hydroxybenzoic acid) and conjugated (syringic acid) benzoic acids were 26,27% recovered in the urine within 5 h. Cinnamic acids were completely undetected in plasma and only trace amounts were found in the urine. Since, the cinnamic acids escaped absorption early in the gastrointestinal tract, their release and/or metabolism is dependant on the host colonic microbiota. Results indicate that there is a high degree of selective absorption of strawberry phenolic acids into the systemic circulation. If selective absorption of phenolic acids is observed with consumption of other plant-based foods, this is likely to have implications for the bioactive role of these compounds in chronic disease prevention. [source]

Pyrimidine nucleotide and nucleic acid synthesis in embryos and megagametophytes of white spruce (Picea glauca) during germination

PHYSIOLOGIA PLANTARUM, Issue 1 2002
Claudio Stasolla
Pyrimidine nucleotide synthesis was investigated in isolated germinating zygotic embryos and separated megagametophytes of white spruce by following the metabolic fate of 14C-labelled orotic acid, uridine, and uracil, as well as by measuring the activities of the major enzymes participating in nucleotide synthesis. The rate of nucleic acid synthesis in these tissues was also examined by tracer experiments and autoradiographic studies conducted with labelled thymidine, and by conventional light microscopy. From our results, it emerges that changes in the contribution of the de novo and salvage pathways of pyrimidines play an important role during the initial stages of zygotic embryo germination. Preferential utilization of uridine for nucleic acid synthesis, via the salvage pathway, was observed at the onset of germination, before the restoration of a fully functional de novo pathway. Similar metabolic changes, not observed in the gametophytic tissue, were also documented in somatic embryos previously. These alterations of the overall pyrimidine metabolism may represent a strategy for ensuring the germinating embryos with a large nucleotide pool. Utilization of 14C-thymidine for nucleic acid synthesis increased in both dissected embryos and megagametophytes during germination. Autoradiographic and light microscopic studies indicated that soon after imbibition, DNA synthesis was preferentially initiated along the embryonic axis, especially in the cortical cells. Apical meristem reactivation was a later event, and the root meristem became activated before the shoot meristem. Taken together, these results indicate that precise changes in nucleotide and nucleic acid metabolism occur during the early phases of embryo germination. [source]

Arylazoamidoximes and Related Compounds as NO-modulators

ARCHIV DER PHARMAZIE, Issue 1 2010
Alexander Schröder
Abstract Three amidinoarylhydrazines 1, three arylazoamidines 2, and nine arylazoamidoximes 3 have been synthesized and investigated for their potential to function as nitric oxide (NO) modulators. In-vitro studies demonstrated that 2 and 3 inhibited platelet aggregation (2c, IC50 = 3 ,M) which could also be shown in vivo by inhibition of thrombus formation in arterioles (3a, 22%). Moreover, for all compounds antihypertensive effects were examined in vivo with SHR rats, with 2a being the most potent candidate by lowering blood pressure by 19%. However, no common underlying mechanism of action could be shown. Some of these compounds released HNO non-enzymatically. Incubations with NO synthase isoforms (NOSs) revealed, that compounds 1 to 3 were weak substrates for NOSs but arylazoamidoximes 3 remarkably elevated the NOSs activity in the presence of L -arginine (3h, up to fivefold). In addition, we examined effects on arginase and dimethylarginine dimethylaminohydrolase (DDAH), two further enzymes involved in the complex regulation of NO biosynthesis, to elucidate whether the observed in-vivo effects can be traced back to their modulation. Furthermore, the metabolic fate of arylazoamidoximes 3 was addressed by investigation of a possible N -reductive biotransformation. In summary, novel NO-modulating compound classes are presented, among which arylazoamidoximes 3 are potent activators of NOS isoforms, and arylazoamidines 2 exert in-vivo effects by unknown mechanisms. [source]

Type 1 diabetes: can exercise impair the autoimmune event?

CELL BIOCHEMISTRY AND FUNCTION, Issue 4 2008
The L -arginine/glutamine coupling hypothesis
Abstract Prevention of type 1 diabetes mellitus (T1DM) requires early intervention in the autoimmune process directed against ,-cells of the pancreatic islets of Langerhans, which is believed to result from a disorder of immunoregulation. According to this concept, a T-helper lymphocyte of type 1 (Th1) subset of T-lymphocytes and their cytokine products, the type 1 cytokines [e.g. interleukin 2 (IL-2), interferon gamma (IFN-,) and tumour necrosis factor beta (TNF-,)] prevail over immunoregulatory (anti-inflammatory) Th2 subset and its cytokine products, i.e. type 2 cytokines (e.g. IL-4, IL-6 and IL-10). This allows type 1 cytokines to initiate a cascade of immune/inflammatory processes in the islet (insulitis), culminating in ,-cell destruction. Activation of sympathetic-corticotropin-releasing hormone (CRH) axis by psychological stress induces specifically Th1 cell overactivity that determines enhanced glutamine utilization and consequent poor L -arginine supply for nitric oxide (NO)-assisted insulin secretion. This determines the shift of intraislet glutamate metabolism from the synthesis of glutathione (GSH) to that of L -arginine, leading to a redox imbalance that activates nuclear factor ,B exacerbating inflammation and NO-mediated cytotoxicity. Physical exercise is capable of inducing changes in the pattern of cytokine production and release towards type 2 class and to normalize the glutamine supply to the circulation, which reduces the need for glutamate, whose metabolic fate may be restored in the direction of GSH synthesis and antioxidant defence. Also, the 70-kDa heat shock protein (hsp70), which is immunoregulatory, may modulate exercise-induced anti-inflammation. In this work, we envisage how exercise can intervene in the mechanisms involved in the autoimmune process against ,-cells and how novel therapeutic approaches may be inferred from these observations. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Neuroexcitatory Effects Of Morphine And Hydromorphone: Evidence Implicating The 3-Glucuronide Metabolites

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 7 2000
Mt Smith
SUMMARY 1. Morphine is recommended by the World Health Organization as the drug of choice for the management of moderate to severe cancer pain. 2. Education of health professionals in the past decade has resulted in a large increase in the prescribing of opioids, such as morphine, and in the magnitude of the doses administered, resulting in an improvement in the quality of pain relief available for many cancer patients. 3. However, the reported incidence of neuroexcitatory side effects (allodynia, myoclonus, seizures) in patients administered large doses of systemic morphine or its structural analogue, hydromorphone (HMOR), has also increased. 4. Clinically, increasing the magnitude of the morphine or HMOR dose administered to patients already exhibiting neuroexcitatory opioid related side effects, results in an exacerbation rather than an attenuation of the excitatory behaviours. 5. In contrast, cessation of the opioid or rotation to a structurally dissimilar opioid (e.g. from morphine/HMOR to methadone or fentanyl), usually results in a restoration of analgesia and resolution of the neuroexcitatory opioid side effects over a period of hours to days. 6. To explain the clinical success of ,opioid rotation', it is essential to understand the in vivo metabolic fate of morphine and HMOR. 7. Following systemic administration, morphine and HMOR are metabolized primarily to the corresponding 3-glucuronide metabolites, morphine-3-glucuronide (M3G) and hydromorphone-3-glucuronide (H3G), which are not only devoid of analgesic activity but evoke a range of dose-dependent excitatory behaviours, including allodynia, myoclonus and seizures, following intracerebroventricular (i.c.v.) administration to rats. 8. Several studies have shown that, following chronic oral or subcutaneous morphine administration to patients with cancer pain, the cerebrospinal fluid (CSF) concentrations of M3G exceed those of morphine and morphine-6-glucuronide (analgesically active morphine metabolite) by approximately two- and five-fold, respectively. 9. These findings suggest that when the M3G concentration (or H3G by analogy) in the CSF exceeds the neuroexcitatory threshold, excitatory behaviours will be evoked in patients. 10. Thus, rotation of the opioid from morphine/HMOR to a structurally dissimilar opioid, such as methadone or fentanyl, will allow clearance of M3G/H3G from the patient central nervous system over hours to days, thereby producing a time-dependent resolution of the neuroexcitatory behaviours while maintaining analgesia with methadone or fentanyl. [source]

Gene expression associated with N-induced shifts in resource allocation in poplar

PLANT CELL & ENVIRONMENT, Issue 5 2003
J. E. K. COOKE
ABSTRACT Surprisingly little is known about molecular mechanisms by which nitrogen (N) availability acts to modulate the growth of forest trees. To address this issue, differential display was used in conjunction with filter-based arrays to identify 52 partial cDNA clones that were significantly regulated within days in response to limiting or luxuriant levels of NH4NO3 fertilization in Populus trichocarpa Torr. & Gray × deltoides Bartr. ex Marsh. A subset of these cDNAs also demonstrated shifts in expression patterns in stem-girdled trees, a manipulative physiology technique that disrupts phloem transport. Stem girdling also induced changes in glutamine and asparagine pools which were correlated with the observed changes in expression profiles for these genes. The identity of these genes provides insight into biochemical processes that are altered by N availability in poplar. Carbon,nitrogen interactions appear to figure prominently in the N-response. The gene expression data suggest that N availability modulates the partitioning of C and N resources into metabolic fates that have the potential to alter both wood quality and quantity, including synthesis of vegetative storage proteins, cell wall components, and terpenoids. [source]

Human urinary metabolite profile of tea polyphenols analyzed by liquid chromatography/electrospray ionization tandem mass spectrometry with data-dependent acquisition

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2008
Shengmin Sang
Tea is rich in polyphenols and has a variety of biological activities. In order to better understand the biological effects of tea constituents on human health, markers for their exposure and their metabolic fates are needed. Previously, we have characterized several catechin metabolites in the blood and urine, but more information on the metabolite profile of tea polyphenols is needed. In the present study, the human urinary metabolite profile of tea polyphenols was investigated using liquid chromatography/electrospray ionization tandem mass spectrometry with data-dependent acquisition. With data-dependent MS/MS analysis by collecting the MS2 and MS3 spectra of the most intense ions in the sample, we identified more than twenty metabolites of tea polyphenols from human urine samples. (,)-Epigallocatechin (EGC) glucuronide, methylated EGC glucuronide, methylated EGC sulfate, (,)-epicatechin (EC) glucruronide, EC sulfate, methylated EC sulfate, as well as the glucuronide and sulfate metabolites of the ring-fission metabolites of tea catechins, 5-(3,,4,,5,-trihydroxyphenyl)- , -valerolactone (M4), 5-(3,,4,-dihydroxyphenyl)- , -valerolactone (M6) and 5-(3,,5,-dihydroxyphenyl)- , -valerolactone (M6,), were the major human urinary metabolites of tea polyphenols. To our knowledge, this is the first report of the direct simultaneous analysis of the human urinary metabolite profile of tea polyphenols using single sample analysis. This method can also be used for thorough investigations of the metabolite profiles of many other dietary constituents. Copyright © 2008 John Wiley & Sons, Ltd. [source]