D. André d'Avignon

Rapid vacuolar sequestration: the horseweed glyphosate resistance mechanism.

BACKGROUND Glyphosate-resistant (GR) weed species are now found with increasing frequency and threaten the critically important glyphosate weed-management system [corrected]. RESULTS The reported (31)P NMR experiments on glyphosate-sensitive (S) and glyphosate-resistant (R) horseweed, Conyza canadensis (L.) Cronq., show significantly more accumulation of glyphosate within the R biotype vacuole. CONCLUSIONS Selective sequestration of glyphosate into the vacuole confers the observed horseweed resistance to glyphosate. This observation represents the first clear evidence for the glyphosate resistance mechanism in C. canadensis.

Adaptation of myocardial substrate metabolism to a ketogenic nutrient environment

Heart muscle is metabolically versatile, converting energy stored in fatty acids, glucose, lactate, amino acids, and ketone bodies. Here, we use mouse models in ketotic nutritional states (24 h of fasting and a very low carbohydrate ketogenic diet) to demonstrate that heart muscle engages a metabolic response that limits ketone body utilization. Pathway reconstruction from microarray data sets, gene expression analysis, protein immunoblotting, and immunohistochemical analysis of myocardial tissue from nutritionally modified mouse models reveal that ketotic states promote transcriptional suppression of the key ketolytic enzyme, succinyl-CoA:3-oxoacid CoA transferase (SCOT; encoded by Oxct1), as well as peroxisome proliferator-activated receptor α-dependent induction of the key ketogenic enzyme HMGCS2. Consistent with reduction of SCOT, NMR profiling demonstrates that maintenance on a ketogenic diet causes a 25% reduction of myocardial 13C enrichment of glutamate when 13C-labeled ketone bodies are delivered in vivo or ex vivo, indicating reduced procession of ketones through oxidative metabolism. Accordingly, unmetabolized substrate concentrations are higher within the hearts of ketogenic diet-fed mice challenged with ketones compared with those of chow-fed controls. Furthermore, reduced ketone body oxidation correlates with failure of ketone bodies to inhibit fatty acid oxidation. These results indicate that ketotic nutrient environments engage mechanisms that curtail ketolytic capacity, controlling the utilization of ketone bodies in ketotic states.

Obligate Role for Ketone Body Oxidation in Neonatal Metabolic Homeostasis

To compensate for the energetic deficit elicited by reduced carbohydrate intake, mammals convert energy stored in ketone bodies to high energy phosphates. Ketone bodies provide fuel particularly to brain, heart, and skeletal muscle in states that include starvation, adherence to low carbohydrate diets, and the neonatal period. Here, we use novel Oxct1−/− mice, which lack the ketolytic enzyme succinyl-CoA:3-oxo-acid CoA-transferase (SCOT), to demonstrate that ketone body oxidation is required for postnatal survival in mice. Although Oxct1−/− mice exhibit normal prenatal development, all develop ketoacidosis, hypoglycemia, and reduced plasma lactate concentrations within the first 48 h of birth. In vivo oxidation of 13C-labeled β-hydroxybutyrate in neonatal Oxct1−/− mice, measured using NMR, reveals intact oxidation to acetoacetate but no contribution of ketone bodies to the tricarboxylic acid cycle. Accumulation of acetoacetate yields a markedly reduced β-hydroxybutyrate:acetoacetate ratio of 1:3, compared with 3:1 in Oxct1+ littermates. Frequent exogenous glucose administration to actively suckling Oxct1−/− mice delayed, but could not prevent, lethality. Brains of newborn SCOT-deficient mice demonstrate evidence of adaptive energy acquisition, with increased phosphorylation of AMP-activated protein kinase α, increased autophagy, and 2.4-fold increased in vivo oxidative metabolism of [13C]glucose. Furthermore, [13C]lactate oxidation is increased 1.7-fold in skeletal muscle of Oxct1−/− mice but not in brain. These results indicate the critical metabolic roles of ketone bodies in neonatal metabolism and suggest that distinct tissues exhibit specific metabolic responses to loss of ketone body oxidation.

Inhibition of Taq polymerase as a method for screening heparin for oversulfated contaminants

Heparin and low molecular heparins are extensively used in the treatment of a wide range of diseases in addition to their classic anticoagulant activity and can be found coating medical devices such as catheters, stents and filters. Early in 2008, a sharp increase in heparin-associated severe adverse events, including over 80 deaths, was linked to the presence of a contaminant identified as hypersulfated chondroitin sulfate (OS-CS). OS-CS is one of several oversulfated glycosaminoglycans (GAGs) of different origins that can potentially cause similar clinical problems underscoring the need to develop robust screening methods for contaminants in existing and future lots of heparin. This study demonstrates that oversulfated GAGs block the activity of Taq polymerase used for real time PCR. Based on this finding we developed a simple, rapid, sensitive and high throughput screening method to detect and quantify oversulfated chondroitin sulfate (OS-CS) and other potential oversulfated contaminants in commercial lots of heparin. This method requires less than 100 miliUnits (mU) of heparin as starting material, therefore avoiding the need to lyophilize and concentrate samples, and has a limit of detection of <1 ng for all oversulfated GAGs tested.

Bayesian analysis of time-domain magnetic resonance signals

Although the discrete Fourier transform remains the dominant means of processing NMR data (l-4), other methods of analyzing time-domain signals exist (5), and there has been recent interest among magnetic resonance scientists in applying alternative analysis techniques in an effort to improve signal-to-noise and resolution of the resulting frequency-domain spectrum. Recently, Bretthorst (6) and Jaynes ( 7) introduced a novel approach to the general time-domain signal analysis problem utilizing the techniques of Bayesian probability theory. Their approach is particularly suited to the class of time-domain signals characteristic of pulsed magnetic resonance spectroscopy, namely, a sum of decaying sinusoids. An especially attractive feature of Bayesian spectrum analysis lies in its ability to integrate out of the parameteroptimization-search procedure many of the parameters that define the model (socalled “nuisance” parameters), This greatly reduces the complexity of the optimization-search process. These nuisance parameters, such as sinusoid amplitude and phase, are then readily estimated, if needed, once the primary model parameters (e.g., frequencies and decay rates) are found via standard optimization-search algorithms. In this communication we demonstrate the application of Bayesian spectrum analysis to a time-domain (Bloch decay) 13C NMR signal from a standard ASTM reference sample of 1,4-dioxane in benzenede. Generally, a substantial amount of prior information is available regarding the “true” signal resulting from an NMR experiment. Making use of this information ought to improve our results. However, simply taking the Fourier transform of the data affords no way to take it into account. This information can be incorporated advantageously into the time-domain analysis, yielding a more powerful parameter determination. In the Bayesian spectrum-analysis and parameter-estimation technique, one analyzes the data in terms of some model which expresses the prior information. The data are fitted to the model using probability theory to obtain the “best” estimated parameters. The residuals are then reviewed to see if there is any coherent characteristic that has not been accounted for in the model. If there is, the model is updated and the entire process repeated until all coherent characteristics are removed from the residuals, that is, until the data accurately map onto the model. The Bayesian analysis gives a simple and elegant interpretation to the model-fitting problem and places the discrete Fourier transform in a new light. When fitting data to a model, the data may be thought of as a vector in an N-dimensional vector space

Successful adaptation to ketosis by mice with tissue-specific deficiency of ketone body oxidation.

During states of low carbohydrate intake, mammalian ketone body metabolism transfers energy substrates originally derived from fatty acyl chains within the liver to extrahepatic organs. We previously demonstrated that the mitochondrial enzyme coenzyme A (CoA) transferase [succinyl-CoA:3-oxoacid CoA transferase (SCOT), encoded by nuclear Oxct1] is required for oxidation of ketone bodies and that germline SCOT-knockout (KO) mice die within 48 h of birth because of hyperketonemic hypoglycemia. Here, we use novel transgenic and tissue-specific SCOT-KO mice to demonstrate that ketone bodies do not serve an obligate energetic role within highly ketolytic tissues during the ketogenic neonatal period or during starvation in the adult. Although transgene-mediated restoration of myocardial CoA transferase in germline SCOT-KO mice is insufficient to prevent lethal hyperketonemic hypoglycemia in the neonatal period, mice lacking CoA transferase selectively within neurons, cardiomyocytes, or skeletal myocytes are all viable as neonates. Like germline SCOT-KO neonatal mice, neonatal mice with neuronal CoA transferase deficiency exhibit increased cerebral glycolysis and glucose oxidation, and, while these neonatal mice exhibit modest hyperketonemia, they do not develop hypoglycemia. As adults, tissue-specific SCOT-KO mice tolerate starvation, exhibiting only modestly increased hyperketonemia. Finally, metabolic analysis of adult germline Oxct1(+/-) mice demonstrates that global diminution of ketone body oxidation yields hyperketonemia, but hypoglycemia emerges only during a protracted state of low carbohydrate intake. Together, these data suggest that, at the tissue level, ketone bodies are not a required energy substrate in the newborn period or during starvation, but rather that integrated ketone body metabolism mediates adaptation to ketogenic nutrient states.

New routes to conformationally restricted peptide building blocks: a convenient preparation of bicyclic piperazinone derivatives

Abstract A facile route for the synthesis of peptide building blocks that constrain the peptide backbone with a 1,4-diazabicyclo[4.3.0]nonane ring skeleton is reported. The synthesis employed an anodic amide oxidation based approach for generating a functionalized proline derivative, and then utilized the derivative as a general substrate for rapidly assembling the bicyclic ring system.

Impact of Peripheral Ketolytic Deficiency on Hepatic Ketogenesis and Gluconeogenesis during the Transition to Birth

Background: SCOT-KO mice cannot oxidize ketone bodies and die within 48 h of birth, due to hyperketonemic hypoglycemia. Results: After suckling milk, livers of SCOT-KO mice develop diminished pyruvate pools and alterations of hepatic pyruvate, fatty acid, and ketone body metabolism. Conclusion: Extrahepatic ketone oxidation supports hepatic adaptation to the extrauterine environment. Significance: Neonatal ketone metabolism reveals the importance of dynamic interorgan metabolic interactions. Preservation of bioenergetic homeostasis during the transition from the carbohydrate-laden fetal diet to the high fat, low carbohydrate neonatal diet requires inductions of hepatic fatty acid oxidation, gluconeogenesis, and ketogenesis. Mice with loss-of-function mutation in the extrahepatic mitochondrial enzyme CoA transferase (succinyl-CoA:3-oxoacid CoA transferase, SCOT, encoded by nuclear Oxct1) cannot terminally oxidize ketone bodies and develop lethal hyperketonemic hypoglycemia within 48 h of birth. Here we use this model to demonstrate that loss of ketone body oxidation, an exclusively extrahepatic process, disrupts hepatic intermediary metabolic homeostasis after high fat mothers milk is ingested. Livers of SCOT-knock-out (SCOT-KO) neonates induce the expression of the genes encoding peroxisome proliferator-activated receptor γ co-activator-1a (PGC-1α), phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase, and glucose-6-phosphatase, and the neonates pools of gluconeogenic alanine and lactate are each diminished by 50%. NMR-based quantitative fate mapping of 13C-labeled substrates revealed that livers of SCOT-KO newborn mice synthesize glucose from exogenously administered pyruvate. However, the contribution of exogenous pyruvate to the tricarboxylic acid cycle as acetyl-CoA is increased in SCOT-KO livers and is associated with diminished terminal oxidation of fatty acids. After mothers milk provokes hyperketonemia, livers of SCOT-KO mice diminish de novo hepatic β-hydroxybutyrate synthesis by 90%. Disruption of β-hydroxybutyrate production increases hepatic NAD+/NADH ratios 3-fold, oxidizing redox potential in liver but not skeletal muscle. Together, these results indicate that peripheral ketone body oxidation prevents hypoglycemia and supports hepatic metabolic homeostasis, which is critical for the maintenance of glycemia during the adaptation to birth.

Impairments of hepatic gluconeogenesis and ketogenesis in PPARα-deficient neonatal mice.

Peroxisome proliferator activated receptor-α (PPARα) is a master transcriptional regulator of hepatic metabolism and mediates the adaptive response to fasting. Here, we demonstrate the roles for PPARα in hepatic metabolic adaptations to birth. Like fasting, nutrient supply is abruptly altered at birth when a transplacental source of carbohydrates is replaced by a high-fat, low-carbohydrate milk diet. PPARα-knockout (KO) neonatal mice exhibit relative hypoglycemia due to impaired conversion of glycerol to glucose. Although hepatic expression of fatty acyl-CoA dehydrogenases is imparied in PPARα neonates, these animals exhibit normal blood acylcarnitine profiles. Furthermore, quantitative metabolic fate mapping of the medium-chain fatty acid [(13)C]octanoate in neonatal mouse livers revealed normal contribution of this fatty acid to the hepatic TCA cycle. Interestingly, octanoate-derived carbon labeled glucose uniquely in livers of PPARα-KO neonates. Relative hypoketonemia in newborn PPARα-KO animals could be mechanistically linked to a 50% decrease in de novo hepatic ketogenesis from labeled octanoate. Decreased ketogenesis was associated with diminished mRNA and protein abundance of the fate-committing ketogenic enzyme mitochondrial 3-hydroxymethylglutaryl-CoA synthase (HMGCS2) and decreased protein abundance of the ketogenic enzyme β-hydroxybutyrate dehydrogenase 1 (BDH1). Finally, hepatic triglyceride and free fatty acid concentrations were increased 6.9- and 2.7-fold, respectively, in suckling PPARα-KO neonates. Together, these findings indicate a primary defect of gluconeogenesis from glycerol and an important role for PPARα-dependent ketogenesis in the disposal of hepatic fatty acids during the neonatal period.

19F-NMR studies of retinol transfer between cellular retinol binding proteins and phospholipid vesicles

The cellular retinol binding proteins, CRBP and CRBP II, are implicated in the cellular uptake of retinol and intracellular trafficking of retinol between sites of metabolic processing. 19F‐NMR studies of retinol transfer between CRBP and CRBP II and phospholipid vesicles, using either fluorine‐labeled ligand or protein, demonstrated that there was significantly more transfer of retinol from CRBP II to lipid vesicles than from CRBP. Differences in how readily protein‐bound retinol is released to lipid bilayers may lead to differences in how these two proteins modulate intracellular retinol metabolism.