BCAA-nitrogen flux in brown fat controls metabolic health independent of thermogenesis.

Brown adipose tissue (BAT) is best known for thermogenesis. Rodent studies demonstrated that enhanced BAT thermogenesis is tightly associated with increased energy expenditure, reduced body weight, and improved glucose homeostasis. However, human BAT is protective against type 2 diabetes, independent of body weight. The mechanism underlying this dissociation remains unclear. Here, we report that impaired mitochondrial catabolism of branched-chain amino acids (BCAAs) in BAT, by deleting mitochondrial BCAA carriers (MBCs), caused systemic insulin resistance without affecting energy expenditure and body weight. Brown adipocytes catabolized BCAA in the mitochondria as nitrogen donors for the biosynthesis of non-essential amino acids and glutathione. Impaired mitochondrial BCAA-nitrogen flux in BAT resulted in increased oxidative stress, decreased hepatic insulin signaling, and decreased circulating BCAA-derived metabolites. A high-fat diet attenuated BCAA-nitrogen flux and metabolite synthesis in BAT, whereas cold-activated BAT enhanced the synthesis. This work uncovers a metabolite-mediated pathway through which BAT controls metabolic health beyond thermogenesis.

Paradoxical activation of transcription factor SREBP1c and de novo lipogenesis by hepatocyte-selective ATP-citrate lyase depletion in obese mice.

Hepatic steatosis associated with high-fat diet, obesity, and type 2 diabetes is thought to be the major driver of severe liver inflammation, fibrosis, and cirrhosis. Cytosolic acetyl CoA (AcCoA), a central metabolite and substrate for de novo lipogenesis (DNL), is produced from citrate by ATP-citrate lyase (ACLY) and from acetate through AcCoA synthase short chain family member 2 (ACSS2). However, the relative contributions of these two enzymes to hepatic AcCoA pools and DNL rates in response to high-fat feeding are unknown. We report here that hepatocyte-selective depletion of either ACSS2 or ACLY caused similar 50% decreases in liver AcCoA levels in obese mice, showing that both pathways contribute to the generation of this DNL substrate. Unexpectedly however, the hepatocyte ACLY depletion in obese mice paradoxically increased total DNL flux measured by D2O incorporation into palmitate, whereas in contrast, ACSS2 depletion had no effect. The increase in liver DNL upon ACLY depletion was associated with increased expression of nuclear sterol regulatory element-binding protein 1c and of its target DNL enzymes. This upregulated DNL enzyme expression explains the increased rate of palmitate synthesis in ACLY-depleted livers. Furthermore, this increased flux through DNL may also contribute to the observed depletion of AcCoA levels because of its increased conversion to malonyl CoA and palmitate. Together, these data indicate that in fat diet-fed obese mice, hepatic DNL is not limited by its immediate substrates AcCoA or malonyl CoA but rather by activities of DNL enzymes.

A high-fat diet increases hepatic mitochondrial turnover through restricted acetylation in a NAFLD mouse model.

Lysine acetylation of proteins has emerged as a key posttranslational modification (PTM) that regulates mitochondrial metabolism. Acetylation may regulate energy metabolism by inhibiting and affecting the stability of metabolic enzymes and oxidative phosphorylation (OxPhos) subunits. Although protein turnover can be easily measured, due to the low abundance of modified proteins, it has been difficult to evaluate the effect of acetylation on the stability of proteins in vivo. We applied 2H2O-metabolic labeling coupled with immunoaffinity and high-resolution mass spectrometry method to measure the stability of acetylated proteins in mouse liver based on their turnover rates. As a proof-of-concept, we assessed the consequence of high-fat diet (HFD)-induced altered acetylation in protein turnover in LDL receptor-deficient (LDLR-/-) mice susceptible to diet-induced nonalcoholic fatty liver disease (NAFLD). HFD feeding for 12 wk led to steatosis, the early stage of NAFLD. A significant reduction in acetylation of hepatic proteins was observed in NAFLD mice, based on immunoblot analysis and label-free quantification with mass spectrometry. Compared with control mice on a normal diet, NAFLD mice had overall increased turnover rates of hepatic proteins, including mitochondrial metabolic enzymes (0.159 ± 0.079 vs. 0.132 ± 0.068 day-1), suggesting their reduced stability. Also, acetylated proteins had slower turnover rates (increased stability) than native proteins in both groups (0.096 ± 0.056 vs. 0.170 ± 0.059 day-1 in control, and 0.111 ± 0.050 vs. 0.208 ± 0.074 day-1 in NAFLD). Furthermore, association analysis revealed a relationship between the HFD-induced decrease in acetylation and increased turnover rates for hepatic proteins in NAFLD mice. These changes were associated with increased expressions of the hepatic mitochondrial transcriptional factor (TFAM) and complex II subunit without any changes to other OxPhos proteins, suggesting that enhanced mitochondrial biogenesis prevented restricted acetylation-mediated depletion of mitochondrial proteins. We conclude that decreased acetylation of mitochondrial proteins may contribute to adaptive improved hepatic mitochondrial function in the early stages of NAFLD.NEW & NOTEWORTHY This is the first method to quantify acetylome dynamics in vivo. This method revealed acetylation-mediated altered hepatic mitochondrial protein turnover in response to a high-fat diet in a mouse model of NAFLD.

Ischemia promotes acyl-CoAs dephosphorylation and propionyl-CoA accumulation.

INTRODUCTION: Our untargeted metabolic data unveiled that Acyl-CoAs undergo dephosphorylation, however little is known about these novel metabolites and their physiology/pathology relevance. OBJECTIVES: To understand the relationship between acyl-CoAs dephosphorylation and energy status as implied in our previous work, we seek to investigate how ischemia (energy depletion) triggers metabolic changes, specifically acyl-CoAs dephosphorylation in this work. METHODS: Rat hearts were isolated and perfused in Langendorff mode for 15 min followed by 0, 5, 15, and 30 minutes of global ischemia. The heart tissues were harvested for metabolic analysis. RESULTS: As expected, ATP and phosphocreatine were significantly decreased during ischemia. Most short- and medium-chain acyl-CoAs progressively increased with ischemic time from 0 to 15 min, whereas a 30-minute ischemia did not lead to further change. Unlike other acyl-CoAs, propionyl-CoA accumulated progressively in the hearts that underwent ischemia from 0 to 30 min. Progressive dephosphorylation occurred to all assayed acyl-CoAs and free CoA regardless their level changes during the ischemia. CONCLUSION: The present work further confirms that dephosphorylation of acyl-CoAs is an energy-dependent process and how this dephosphorylation is mediated warrants further investigations. It is plausible that dephosphorylation of acyl-CoAs and limited anaplerosis are involved in ischemic injuries to heart. Further investigations are warranted to examine the mechanisms of acyl-CoA dephosphorylation and how the dephosphorylation is possibly involved in ischemic injuries.

The intestine is a major contributor to circulating succinate in mice.

The tricarboxylic acid (TCA) cycle is the epicenter of cellular aerobic metabolism. TCA cycle intermediates facilitate energy production and provide anabolic precursors, but also function as intra- and extracellular metabolic signals regulating pleiotropic biological processes. Despite the importance of circulating TCA cycle metabolites as signaling molecules, the source of circulating TCA cycle intermediates remains uncertain. We observe that in mice, the concentration of TCA cycle intermediates in the portal blood exceeds that in tail blood indicating that the gut is a major contributor to circulating TCA cycle metabolites. With a focus on succinate as a representative of a TCA cycle intermediate with signaling activities and using a combination of gut microbiota depletion mouse models and isotopomer tracing, we demonstrate that intestinal microbiota is not a major contributor to circulating succinate. Moreover, we demonstrate that endogenous succinate production is markedly higher than intestinal succinate absorption in normal physiological conditions. Altogether, these results indicate that endogenous succinate production within the intestinal tissue is a major physiological source of circulating succinate. These results provide a foundation for an investigation into the role of the intestine in regulating circulating TCA cycle metabolites and their potential signaling effects on health and disease.

First Report of Leaf Spot Caused by Botrytis cinerea on Strawberry in China.

In the winter of 2022, circular or irregular leaf spots were observed on strawberry (Fragaria × ananassa) planted in commercial fields (cultivar 'xuetu', 'mengzhifu') in Yinzhou, Ningbo, Zhejiang, China (N29°48'48″, E121°39'47″), with disease incidence ranging from 10 to 15% in a field approximately 0.67 ha in size. The estimated crop loss associated with this disease was ~10%. Symptoms included circular or irregular lesions with brown halos and wheel marks, which eventually developed into leaf blight and petiole decay, but spore masses were seldom found on the leaf surface. In severe cases, leaves withered and abscissed. To isolate the causal agent, ten diseased leaves from ten different plants were collected, surface-sterilized with 75% ethanol for 50 s, rinsed twice with sterile distilled water, cut into small pieces (0.5 cm × 0.5 cm), and plated on potato dextrose agar (PDA), then incubated at 25°C in darkness for 5 days. Isolates , which displayed one kind of colony morphology were consistently obtained from each of the ten samples, and 58 single-conidium isolates with the same colony morphology were obtained. The isolation frequency was 58 of 60 samples. The colonies that grew on PDA produced white mycelia, which sporulated after 1 week, producing typical Botrytis-like gray spores. Three isolates (NBCM-1, NBCM-2, NBCM-3) were selected for identification and pathogenicity assays. Conidia were round to ellipsoid, 9.2 to 14.3 µm long (n=50), and 6.4 to 9.2 µm wide (n=50). Sclerotia were not observed on PDA. Based on these characteristics, the pathogen was tentatively identified as Botrytis cinerea (Zhang 2001). PCR was conducted for each of the three isolates to amplify the G3PDH, HSP60, RPB2, NEP1, and NEP2 genes, which are typically used for molecular identification of Botrytis species (Staats et al. 2005; Liu et al. 2016). The resulting amplicons were sequenced, and the sequences were processed using BLAST in the National Center for Biotechnology Information. Sequences of the three isolates were deposited in GenBank (accession nos. OR052082 to OR052086, OR493405 to OR493414). BLASTn analyses showed that isolates were 99 to 100% identical to B.cinerea reported causing leaf spot on strawberry in California; accession numbers MK919496 (G3PDH, 883/883 bp), MK919494 (HSP60, 992/992 bp), and MK919495 (RPB2, 1081/1081 bp). The resulting concatenated data set of G3PDH-HSP60-RPB2-NEP1-NEP2 was used to conduct a multilocus phylogenetic analysis (MLSA) using the maximum likelihood method. The MLSA tree indicated that the three isolates belonged to Botrytis cinerea. To test for pathogenicity, three 1-month-old strawberry (cultivar 'xuetu') plants were inoculated with each isolate (NBCM-1, NBCM-2, NBCM-3). A noninoculated control (sterile water only) was also included. The strawberry plants were inoculated by spraying with conidia suspension (1.0 × 105/ml) until run-off. Inoculations with sterile water served as controls. All plants were kept at 28/25°C (day/night), under a 12:12-h light/dark photoperiod. All plants were covered with transparent plastic bags to maintain humidity for the first 48 h, after which the bags were removed. After 4 to 7 days, leaf spot symptoms similar to those observed in the field were observed in all inoculated plants, while the controls remained healthy. The experiment was repeated three times. The pathogen was reisolated from the inoculated leaves and again identified as B. cinerea, with the same methodology used for the initial identification. Leaf spot caused by B. cinerea on strawberry was recently reported in California (Mansouripour and Holmes 2020) and Florida (Marin and Peres 2022). To our knowledge, this is the first report of B. cinerea causing leaf spot on strawberry in China. The pathogen is also the causal agent of Botrytis fruit rot on strawberry. Given the high variability of this pathogen (Marin and Peres 2022), further studies on its occurrence, spread, management, and control are required. The identification of this pathogen provides a basis for further research on its management and control.

First Report of Pantoea ananatis Causing Crown Necrobiosis on Strawberry in China.

Strawberry (Fragaria × ananassa) is an economically important crop in Zhejiang, China. In the autumn of 2021, crown necrobiosis and angular leaf spot was observed in commercial strawberry fields (cultivar 'fenyu') in Cixi, Ningbo, Zhejiang, China (N30°9'55″, E121°21'13″). The disease incidence ranged from 5 to 8 % in the field, but could reach 50 to 60 % in some heavily affected plastic tunnels. In the affected field, this disease could reduce strawberry production by 50%. Early symptoms were water-soaked lesions around the vein of the abaxial leaves; subsequently, reddish-brown irregular spots and coalesced lesions developed. In humid conditions, a sticky bacterial ooze exuding from lesions was observed. Finally, the crown of the diseased plant was necrotized, and several pockets were observed inside the crown after dissection. To isolate the causal agent, the infected leaves and crown tissues from six different plants were surface-sterilized with 75% ethanol for 1 min, rinsed twice with sterile distilled water, cut into small pieces, and soaked in 5 ml of sterile distilled water for 20 min. The supernatant from the cut-up pieces was serially diluted and spread on nutrient agar medium. After 2 to 3 days at 28℃, several yellow colonies were grown on the medium. The colonies from five infected plants were gram-negative, anaerobic rods, yellow, viscous, and gloss, which are typical characteristics of Erwinia anana (Wells et al. 1986). To confirm the identity of the causal bacteria, PCR was conducted for six randomly selected colonies to amplify 16S rRNA (Monciardini et al. 2002), fusA, and gyrB (Stice et al. 2002). The amplicons were sequenced and blasted, and the results showed that the six colonies were identical. The 16S rRNA, fusA, gyrB sequences of the isolate CM3 were deposited in GenBank with accession number ON754076.1, OP587277, and OP587278; BLAST search showed 99.93% (1445 bp out of 1446 bp), 100% (746 bp out of 746 bp), 99.64% (1371 bp out of 1376 bp) similarity with strains of Pantoea ananatis (KT741001.1, MH015093.1 and CP066803.1 accessions, respectively). The resulting concatenated data set of 16S rRNA-fusA-gyrB was used to build a multilocus phylogenetic analysis (MLSA) by maximum likelihood criteria. The MLSA tree indicated that the isolate CM3 belonged to Pantoea ananatis. The isolate's identity was further confirmed by P. ananatis-specific primers pagyrB-F/R (Xiao et al. 2022). Thus, this isolate was designated as P. ananatis CM3. To fulfill Koch's postulates, two old leaves were broken off each of the ten 2-month-old strawberry (cultivar 'fenyu') plants to create wounds, each plants was sprayed with a cell suspension of P. ananatis (107CFU/ml, 0.5 ml) on the stem base. Ten plants were sprayed with water to serve as a control. All plants were kept at 28/25°C (day/night) under a 12-h/12-h photoperiod. All plants were covered with transparent plastic bags to maintain humidity. After 48 h, the bags were removed. After 2 weeks, water-soaked lesions on some leaves were observed similar to those in the field . Three to five weeks after inoculation, the crown of the inoculated plants was necrotized, which was similar to the symptoms in the field. No symptoms were observed in the control plants. The experiment was repeated three times. The bacteria were successfully reisolated from the inoculated crown tissues and leaves and confirmed as CM3 according to the same methodologies used for the initial identification. Bacterial leaf blight in strawberry caused by Pantoea ananatis has been reported in Nova Scotia, Canada, and Egypt (Bajpai et al. 2019; Abdel-Gaied et al. 2022). To our knowledge, this is the first report of Pantoea ananatis causing crown necrobiosis on strawberry in China. This report provides a basis for further research on this disease and its management and control.

Metabolic perturbations mediated by propionyl-CoA accumulation in organs of mouse model of propionic acidemia.

Propionic acidemia (PA) is an autosomal recessive metabolic disorder after gene encoding propionyl-CoA carboxylase, Pcca or Pccb, is mutated. This genetic disorder could develop various complications which are ascribed to dysregulated propionyl-CoA metabolism in organs. However, the effect of attenuated PCC on propionyl-CoA metabolism in different organs remains to be fully understood. We investigated metabolic perturbations in organs of Pcca-/-(A138T) mice (a mouse model of PA) under chow diet and acute administration of [13C3]propionate to gain insight into pathological mechanisms of PA. With chow diet, the metabolic alteration is organ dependent. l-Carnitine reduction induced by propionylcarnitine accumulation only occurs in lung and liver of Pcca-/- (A138T) mice. [13C3]Propionate tracing data demonstrated that PCC activity was dramatically reduced in Pcca-/-(A138T) brain, lung, liver, kidney, and adipose tissues, but not significantly changed in Pcca-/-(A138T) muscles (heart and skeletal muscles) and pancreas, which was largely supported by PCCA expression data. The largest expansion of propionylcarnitine in Pcca-/-(A138T) heart after acute administration of propionate indicated the vulnerability of heart to high circulating propionate. The overwhelming propionate in blood also stimulated ketone production from the increased fatty acid oxidation in Pcca-/-(A138T) liver by lowering malonyl-CoA, which has been observed in cases where metabolic decompensation occurs in PA patients. This work shed light on organ-specific metabolic alternations under varying severities of PA.

Measuring acetyl-CoA and acetylated histone turnover in vivo: Effect of a high fat diet.

Cellular availability of acetyl-CoA, a central intermediate of metabolism, regulates histone acetylation. The impact of a high-fat diet (HFD) on the turnover rates of acetyl-CoA and acetylated histones is unknown. We developed a method for simultaneous measurement of acetyl-CoA and acetylated histones kinetics using a single 2H2O tracer, and used it to examine effect of HFD-induced perturbations on hepatic histone acetylation in LDLR-/- mice, a mouse model of non-alcoholic fatty liver disease (NAFLD). Mice were given 2H2O in the drinking water and the kinetics of hepatic acetyl-CoA, histones, and acetylated histones were quantified based on their 2H-labeling. Consumption of a high fat Western-diet (WD) for twelve weeks led to decreased acetylation of hepatic histones (p< 0.05), as compared to a control diet. These changes were associated with 1.5-3-fold increased turnover rates of histones without any change in acetyl-CoA flux. Acetylation significantly reduced the stability of histones and the turnover rates of acetylated peptides were correlated with the number of acetyl groups in neighboring lysine sites. We conclude that 2H2O-method can be used to study metabolically controlled histone acetylation and acetylated histone turnover in vivo.

Overcompensation of CoA Trapping by Di(2-ethylhexyl) Phthalate (DEHP) Metabolites in Livers of Wistar Rats.

Di(2-ethylhexyl) phthalate (DEHP) is commonly used as a plasticizer in various industrial and household plastic products, ensuring widespread human exposures. Its routine detection in human bio-fluids and the propensity of its monoester metabolite to activate peroxisome proliferator activated receptor-α (PPARα) and perturb lipid metabolism implicate it as a metabolic disrupter. In this study we evaluated the effects of DEHP exposure on hepatic levels of free CoA and various CoA esters, while also confirming the metabolic activation to CoA esters and partial ß-oxidation of a DEHP metabolite (2-ethyhexanol). Male Wistar rats were exposed via diet to 2% (w/w) DEHP for fourteen-days, following which hepatic levels of free CoA and various CoA esters were identified using liquid chromatography-mass spectrometry. DEHP exposed rats showed significantly elevated free CoA and increased levels of physiological, DEHP-derived and unidentified CoA esters. The physiological CoA ester of malonyl-CoA and DEHP-derived CoA ester of 3-keto-2-ethylhexanoyl-CoA were the most highly elevated, at eighteen- and ninety eight-times respectively. We also detected sixteen unidentified CoA esters which may be derivative of DEHP metabolism or induction of other intermediary metabolism metabolites. Our results demonstrate that DEHP is a metabolic disrupter which affects production and sequestration of CoA, an essential cofactor of oxidative and biosynthetic reactions.

Dietary branched-chain amino acid restriction alters fuel selection and reduces triglyceride stores in hearts of Zucker fatty rats.

Elevations in circulating levels of branched-chain amino acids (BCAAs) are associated with a variety of cardiometabolic diseases and conditions. Restriction of dietary BCAAs in rodent models of obesity lowers circulating BCAA levels and improves whole-animal and skeletal-muscle insulin sensitivity and lipid homeostasis, but the impact of BCAA supply on heart metabolism has not been studied. Here, we report that feeding a BCAA-restricted chow diet to Zucker fatty rats (ZFRs) causes a shift in cardiac fuel metabolism that favors fatty acid relative to glucose catabolism. This is illustrated by an increase in labeling of acetyl-CoA from [1-13C]palmitate and a decrease in labeling of acetyl-CoA and malonyl-CoA from [U-13C]glucose, accompanied by a decrease in cardiac hexokinase II and glucose transporter 4 protein levels. Metabolomic profiling of heart tissue supports these findings by demonstrating an increase in levels of a host of fatty-acid-derived metabolites in hearts from ZFRs and Zucker lean rats (ZLRs) fed the BCAA-restricted diet. In addition, the twofold increase in cardiac triglyceride stores in ZFRs compared with ZLRs fed on chow diet is eliminated in ZFRs fed on the BCAA-restricted diet. Finally, the enzymatic activity of branched-chain ketoacid dehydrogenase (BCKDH) is not influenced by BCAA restriction, and levels of BCAA in the heart instead reflect their levels in circulation. In summary, reducing BCAA supply in obesity improves cardiac metabolic health by a mechanism independent of alterations in BCKDH activity.

Analysis of endophytic bacterial community diversity and metabolic correlation in Cinnamomum camphora.

The structure and diversity of microbial communities in the leaves of Cinnamomum camphora at different growth stages were studied by high-throughput sequencing. Moreover, the relationships between microbial communities and borneol content were analyzed in this paper. The results indicated that the community structure of endophytic bacteria in C. camphora exhibited temporal variations, with the microbial diversity presented as follows: T1 (low content period) > T3 (peak period) > T2 (small peak period). The population of endophytic bacteria and the ratio of primary metabolism in the leaves of C. camphora were T2 > T1 > T3, while the metabolic intensity of endophytic bacterial terpenoids and polyketides was T3 > T2 > T1, which had the same trend as borneol content in C. camphora. The metabolic ratio of terpenoids and polyketides in T3 was 7.44% higher than that in T1, while that in T2 was 4.10% higher than that in T1. The abundance and diversity of Clostridium_sensu_stricto_1, Ochrobactrum, Escherichia-Shigella, Pseudomonas, and Massilia significantly promoted the content of terpenoids in C. camphora. Together, those results provide the first evidence that borneol content and potential metabolic intensity in leaves of C. camphora greatly depend on microbial communities composition and diversity.

Cardiovascular Metabolomics.

Disturbances in cardiac metabolism underlie most cardiovascular diseases. Metabolomics, one of the newer omics technologies, has emerged as a powerful tool for defining changes in both global and cardiac-specific metabolism that occur across a spectrum of cardiovascular disease states. Findings from metabolomics studies have contributed to better understanding of the metabolic changes that occur in heart failure and ischemic heart disease and have identified new cardiovascular disease biomarkers. As technologies advance, the metabolomics field continues to evolve rapidly. In this review, we will discuss the current state of metabolomics technologies, including consideration of various metabolomics platforms and elements of study design; the emerging utility of stable isotopes for metabolic flux studies; and the use of metabolomics to better understand specific cardiovascular diseases, with an emphasis on recent advances in the field.

Propionate-induced changes in cardiac metabolism, notably CoA trapping, are not altered by l-carnitine.

High concentrations of propionate and its metabolites are found in several diseases that are often associated with the development of cardiac dysfunction, such as obesity, diabetes, propionic acidemia, and methylmalonic acidemia. In the present work, we employed a stable isotope-based metabolic flux approach to understand propionate-mediated perturbation of cardiac energy metabolism. Propionate led to accumulation of propionyl-CoA (increased by ~101-fold) and methylmalonyl-CoA (increased by 36-fold). This accumulation caused significant mitochondrial CoA trapping and inhibited fatty acid oxidation. The reduced energy contribution from fatty acid oxidation was associated with increased glucose oxidation. The enhanced anaplerosis of propionate and CoA trapping altered the pool sizes of tricarboxylic acid cycle (TCA) metabolites. In addition to being an anaplerotic substrate, the accumulation of proprionate-derived malate increased the recycling of malate to pyruvate and acetyl-CoA, which can enter the TCA for energy production. Supplementation of 3 mM l-carnitine did not relieve CoA trapping and did not reverse the propionate-mediated fuel switch. This is due to new findings that the heart appears to lack the specific enzyme catalyzing the conversion of short-chain (C3 and C4) dicarboxylyl-CoAs to dicarboxylylcarnitines. The discovery of this work warrants further investigation on the relevance of dicarboxylylcarnitines, especially C3 and C4 dicarboxylylcarnitines, in cardiac conditions such as heart failure.

Quantifying ceramide kinetics in vivo using stable isotope tracers and LC-MS/MS.

Numerous studies have implicated dyslipidemia as a key factor in mediating insulin resistance. Ceramides have received special attention since their levels are inversely associated with normal insulin signaling and positively associated with factors that are involved in cardiometabolic disease. Despite the growing literature surrounding ceramide biology, there are limited data regarding the activity of ceramide synthesis and turnover in vivo. Herein, we demonstrate the ability to measure ceramide kinetics by coupling the administration of [2H]water with LC-MS/MS analyses. As a "proof-of-concept" we determined the effect of a diet-induced alteration on ceramide flux; studies also examined the effect of myriocin (a known inhibitor of serine palmitoyltransferase, the first step in sphingosine biosynthesis). Our data suggest that one can estimate ceramide synthesis and draw conclusions regarding the source of fatty acids; we discuss caveats in regards to method development in this area.

Methylfolate Trap Promotes Bacterial Thymineless Death by Sulfa Drugs.

The methylfolate trap, a metabolic blockage associated with anemia, neural tube defects, Alzheimer's dementia, cardiovascular diseases, and cancer, was discovered in the 1960s, linking the metabolism of folate, vitamin B12, methionine and homocysteine. However, the existence or physiological significance of this phenomenon has been unknown in bacteria, which synthesize folate de novo. Here we identify the methylfolate trap as a novel determinant of the bacterial intrinsic death by sulfonamides, antibiotics that block de novo folate synthesis. Genetic mutagenesis, chemical complementation, and metabolomic profiling revealed trap-mediated metabolic imbalances, which induced thymineless death, a phenomenon in which rapidly growing cells succumb to thymine starvation. Restriction of B12 bioavailability, required for preventing trap formation, using an "antivitamin B12" molecule, sensitized intracellular bacteria to sulfonamides. Since boosting the bactericidal activity of sulfonamides through methylfolate trap induction can be achieved in Gram-negative bacteria and mycobacteria, it represents a novel strategy to render these pathogens more susceptible to existing sulfonamides.

The growth-promoting effects of endophytic bacteria on Phyllostachys edulis.

The research results of the growth-promoting effects of endophytic bacteria on Phyllostachys edulis indicated that the growth-promoting endophytic bacteria could improve photosynthesis in P. edulis leaves. The photosynthetic rate, transpiration rate, and the stomatal conductance in P. edulis treated with endophytic bacteria were all higher than in the control group. Endophytic bacteria could also increase the chlorophyll content and the protective enzyme activities in P. edulis, improving their reactions to the adverse environmental conditions. Through injection treatments with growth-promoting endophytic bacteria, the catalase, superoxide dismutase (SOD), peroxidase activity, soluble protein content, and soluble sugar content in P. edulis were all higher than in the control group, except for the malondialdehyde content, which was lower than in the control group.

Inter-relations between 3-hydroxypropionate and propionate metabolism in rat liver: relevance to disorders of propionyl-CoA metabolism.

Propionate, 3-hydroxypropionate (3HP), methylcitrate, related compounds, and ammonium accumulate in body fluids of patients with disorders of propionyl-CoA metabolism, such as propionic acidemia. Although liver transplantation alleviates hyperammonemia, high concentrations of propionate, 3HP, and methylcitrate persist in body fluids. We hypothesized that conserved metabolic perturbations occurring in transplanted patients result from the simultaneous presence of propionate and 3HP in body fluids. We investigated the inter-relations of propionate and 3HP metabolism in perfused livers from normal rats using metabolomic and stable isotopic technologies. In the presence of propionate, 3HP, or both, we observed the following metabolic perturbations. First, the citric acid cycle (CAC) is overloaded but does not provide sufficient reducing equivalents to the respiratory chain to maintain the homeostasis of adenine nucleotides. Second, there is major CoA trapping in the propionyl-CoA pathway and a tripling of liver total CoA within 1 h. Third, liver proteolysis is stimulated. Fourth, propionate inhibits the conversion of 3HP to acetyl-CoA and its oxidation in the CAC. Fifth, some propionate and some 3HP are converted to nephrotoxic maleate by different processes. Our data have implications for the clinical management of propionic acidemia. They also emphasize the perturbations of the liver intermediary metabolism induced by supraphysiological, i.e., millimolar, concentrations of labeled propionate used to trace the intermediary metabolism, in particular, inhibition of CAC flux and major decreases in the [ATP]/[ADP] and [ATP]/[AMP] ratios.

Identification of S-nitroso-CoA reductases that regulate protein S-nitrosylation.

Coenzyme A (CoA) mediates thiol-based acyl-group transfer (acetylation and palmitoylation). However, a role for CoA in the thiol-based transfer of NO groups (S-nitrosylation) has not been considered. Here we describe protein S-nitrosylation in yeast (heretofore unknown) that is mediated by S-nitroso-CoA (SNO-CoA). We identify a specific SNO-CoA reductase encoded by the alcohol dehydrogenase 6 (ADH6) gene and show that deletion of ADH6 increases cellular S-nitrosylation and alters CoA metabolism. Further, we report that Adh6, acting as a selective SNO-CoA reductase, protects acetoacetyl-CoA thiolase from inhibitory S-nitrosylation and thereby affects sterol biosynthesis. Thus, Adh6-regulated, SNO-CoA-mediated protein S-nitrosylation provides a regulatory mechanism paralleling protein acetylation. We also find that SNO-CoA reductases are present from bacteria to mammals, and we identify aldo-keto reductase 1A1 as the mammalian functional analog of Adh6. Our studies reveal a novel functional class of enzymes that regulate protein S-nitrosylation from yeast to mammals and suggest that SNO-CoA-mediated S-nitrosylation may subserve metabolic regulation.

Compartmentation of Metabolism of the C12-, C9-, and C5-n-dicarboxylates in Rat Liver, Investigated by Mass Isotopomer Analysis: ANAPLEROSIS FROM DODECANEDIOATE.

We investigated the compartmentation of the catabolism of dodecanedioate (DODA), azelate, and glutarate in perfused rat livers, using a combination of metabolomics and mass isotopomer analyses. Livers were perfused with recirculating or nonrecirculating buffer containing one fully (13)C-labeled dicarboxylate. Information on the peroxisomal versus mitochondrial catabolism was gathered from the labeling patterns of acetyl-CoA proxies, i.e. total acetyl-CoA, the acetyl moiety of citrate, C-1 + 2 of ß-hydroxybutyrate, malonyl-CoA, and acetylcarnitine. Additional information was obtained from the labeling patterns of citric acid cycle intermediates and related compounds. The data characterize the partial oxidation of DODA and azelate in peroxisomes, with terminal oxidation in mitochondria. We did not find evidence of peroxisomal oxidation of glutarate. Unexpectedly, DODA contributes a substantial fraction to anaplerosis of the citric acid cycle. This opens the possibility to use water-soluble DODA in nutritional or pharmacological anaplerotic therapy when other anaplerotic substrates are impractical or contraindicated, e.g. in propionic acidemia and methylmalonic acidemia.