Proposal and confirmation of N-(2-carboxyethyl)proline as a human endogenous metabolite

RATIONALE

Malondialdehyde, one of the peroxidation products of polyunsaturated fatty acids, has been widely reported as an oxidative stress biomarker in many diseases. However, malondialdehyde is inherently unstable in biological matrices, which renders its measurement unreliable with all the reported analytical methods. To find an alternative oxidative stress biomarker, we envisioned that N-(2-carboxyethyl)proline, a modified conjugate of malondialdehyde and proline, could be a stable candidate for this purpose.

METHODS

The proposed compound was chemically synthesized, and liquid chromatography-mass spectrometry methods were developed and used to search for the compound in human biological samples.

RESULTS

An endogenous metabolite in human feces and urine samples was found to match the synthetic N-(2-carboxyethyl)proline by chromatographic retention and the fragmentation pattern of its molecular ion.

CONCLUSION

The results confirmed that N-(2-carboxyethyl)proline was a new metabolite in human feces and urine samples. In addition, our results demonstrated a case of successful identification of true unknown metabolite by knowledge-based hypothesis of possible metabolites followed by experimental confirmation with a synthetic standard.

LC-MS/MS method with chemical derivatization for quantitation of L-threonate in human plasma

An LC-MS/MS-based bioanalytical method has been developed to measure the concentration of L-threonate at its endogenous level in human plasma. Following isotope dilution and protein precipitation, the samples were acetylated and chromatographed under reversed-phase conditions for baseline separation of the derivatized L-threonate and its stereoisomer D-erythronate. The method was assessed by a fit-for-purpose validation with a calibration range from 100 to 10,000 ng/mL. The intra-run coefficients of variation (CVs) were <3.6% and the inter-run CV was 3.2% for the QC samples at endogenous level. At the lower limit of quantitation, the intra-run CV was 6.1% and the average inaccuracy was -1.4%. This method provides an efficient and reliable quantitation of L-threonate and could be useful to certain biomarker investigators.

A novel insulin resistance index to monitor changes in insulin sensitivity and glucose tolerance: the ACT NOW study

OBJECTIVE

The objective was to test the clinical utility of Quantose M(Q) to monitor changes in insulin sensitivity after pioglitazone therapy in prediabetic subjects. Quantose M(Q) is derived from fasting measurements of insulin, α-hydroxybutyrate, linoleoyl-glycerophosphocholine, and oleate, three nonglucose metabolites shown to correlate with insulin-stimulated glucose disposal.

RESEARCH DESIGN AND METHODS

Participants were 428 of the total of 602 ACT NOW impaired glucose tolerance (IGT) subjects randomized to pioglitazone (45 mg/d) or placebo and followed for 2.4 years. At baseline and study end, fasting plasma metabolites required for determination of Quantose, glycated hemoglobin, and oral glucose tolerance test with frequent plasma insulin and glucose measurements to calculate the Matsuda index of insulin sensitivity were obtained.

RESULTS

Pioglitazone treatment lowered IGT conversion to diabetes (hazard ratio = 0.25; 95% confidence interval = 0.13-0.50; P < .0001). Although glycated hemoglobin did not track with insulin sensitivity, Quantose M(Q) increased in pioglitazone-treated subjects (by 1.45 [3.45] mg·min(-1)·kgwbm(-1)) (median [interquartile range]) (P < .001 vs placebo), as did the Matsuda index (by 3.05 [4.77] units; P < .0001). Quantose M(Q) correlated with the Matsuda index at baseline and change in the Matsuda index from baseline (rho, 0.85 and 0.79, respectively; P < .0001) and was progressively higher across closeout glucose tolerance status (diabetes, IGT, normal glucose tolerance). In logistic models including only anthropometric and fasting measurements, Quantose M(Q) outperformed both Matsuda and fasting insulin in predicting incident diabetes.

CONCLUSIONS

In IGT subjects, Quantose M(Q) parallels changes in insulin sensitivity and glucose tolerance with pioglitazone therapy. Due to its strong correlation with improved insulin sensitivity and its ease of use, Quantose M(Q) may serve as a useful clinical test to identify and monitor therapy in insulin-resistant patients.

A novel test for IGT utilizing metabolite markers of glucose tolerance

The oral glucose tolerance test (OGTT) is the only method to diagnose patients having impaired glucose tolerance (IGT), but its use has diminished considerably in recent years. Metabolomic profiling studies have identified a number of metabolites whose fasting levels are associated with dysglycemia and type 2 diabetes. These metabolites may serve as the basis of an alternative test for IGT. Using the stable isotope dilution technique, quantitative assays were developed for 23 candidate biomarker metabolites. These metabolites were measured in fasting plasma samples taken just prior to an OGTT from 1623 nondiabetic subjects: 955 from the Relationship between Insulin Sensitivity and Cardiovascular Disease Study (RISC Study; 11.7% IGT) and 668 subjects from the Diabetes Mellitus and Vascular Health Initiative (DMVhi) cohort from the DEXLIFE project (11.8% IGT). The associations between metabolites, anthropometric, and metabolic parameters and 2hPG values were assessed by Pearson correlation coefficients and Random Forest classification analysis to rank variables for their ability to distinguish IGT from normal glucose tolerance (NGT). Multivariate logistic regression models for estimating risk of IGT were developed and evaluated using AUCs calculated from the corresponding ROC curves. A model based on the fasting plasma levels of glucose, α-hydroxybutyric acid, β-hydroxybutyric acid, 4-methyl-2-oxopentanoic acid, linoleoylglycerophosphocholine, oleic acid, serine and vitamin B5 was optimized in the RISC cohort (AUC = 0.82) and validated in the DMVhi cohort (AUC = 0.83). A novel, all-metabolite-based test is shown to be a discriminate marker of IGT. It requires only a single fasted blood draw and may serve as a more convenient surrogate for the OGTT or as a means of identifying subjects likely to be IGT.

Cysteine catabolism: a novel metabolic pathway contributing to glioblastoma growth

The relevance of cysteine metabolism in cancer has gained considerable interest in recent years, largely focusing on its role in generating the antioxidant glutathione. Through metabolomic profiling using a combination of high-throughput liquid and gas chromatography-based mass spectrometry on a total of 69 patient-derived glioma specimens, this report documents the discovery of a parallel pathway involving cysteine catabolism that results in the accumulation of cysteine sulfinic acid (CSA) in glioblastoma. These studies identified CSA to rank as one of the top metabolites differentiating glioblastoma from low-grade glioma. There was strong intratumoral concordance of CSA levels with expression of its biosynthetic enzyme cysteine dioxygenase 1 (CDO1). Studies designed to determine the biologic consequence of this metabolic pathway identified its capacity to inhibit oxidative phosphorylation in glioblastoma cells, which was determined by decreased cellular respiration, decreased ATP production, and increased mitochondrial membrane potential following pathway activation. CSA-induced attenuation of oxidative phosphorylation was attributed to inhibition of the regulatory enzyme pyruvate dehydrogenase. Studies performed in vivo abrogating the CDO1/CSA axis using a lentiviral-mediated short hairpin RNA approach resulted in significant tumor growth inhibition in a glioblastoma mouse model, supporting the potential for this metabolic pathway to serve as a therapeutic target. Collectively, we identified a novel, targetable metabolic pathway involving cysteine catabolism contributing to the growth of aggressive high-grade gliomas. These findings serve as a framework for future investigations designed to more comprehensively determine the clinical application of this metabolic pathway and its contributory role in tumorigenesis.

Metabolomic signatures of aggressive prostate cancer

BACKGROUND

Current diagnostic techniques have increased the detection of prostate cancer; however, these tools inadequately stratify patients to minimize mortality. Recent studies have identified a biochemical signature of prostate cancer metastasis, including increased sarcosine abundance. This study examined the association of tissue metabolites with other clinically significant findings.

METHODS

A state of the art metabolomics platform analyzed prostatectomy tissues (331 prostate tumor, 178 cancer-free prostate tissues) from two independent sites. Biochemicals were analyzed by gas chromatography-mass spectrometry and ultrahigh performance liquid chromatography-tandem mass spectrometry. Statistical analyses identified metabolites associated with cancer aggressiveness: Gleason score, extracapsular extension, and seminal vesicle and lymph node involvement.

RESULTS

Prostate tumors had significantly altered metabolite profiles compared to cancer-free prostate tissues, including biochemicals associated with cell growth, energetics, stress, and loss of prostate-specific biochemistry. Many metabolites were further associated with clinical findings of aggressive disease. Aggressiveness-associated metabolites stratified prostate tumor tissues with high abundances of compounds associated with normal prostate function (e.g., citrate and polyamines) from more clinically advanced prostate tumors. These aggressive prostate tumors were further subdivided by abundance profiles of metabolites including NAD+ and kynurenine. When added to multiparametric nomograms, metabolites improved prediction of organ confinement (AUROC from 0.53 to 0.62) and 5-year recurrence (AUROC from 0.53 to 0.64).

CONCLUSIONS

These findings support and extend earlier metabolomic studies in prostate cancer and studies where metabolic enzymes have been associated with carcinogenesis and/or outcome. Furthermore, these data suggest that panels of analytes may be valuable to translate metabolomic findings to clinically useful diagnostic tests.

Genetic variants associated with glycine metabolism and their role in insulin sensitivity and type 2 diabetes

Circulating metabolites associated with insulin sensitivity may represent useful biomarkers, but their causal role in insulin sensitivity and diabetes is less certain. We previously identified novel metabolites correlated with insulin sensitivity measured by the hyperinsulinemic-euglycemic clamp. The top-ranking metabolites were in the glutathione and glycine biosynthesis pathways. We aimed to identify common genetic variants associated with metabolites in these pathways and test their role in insulin sensitivity and type 2 diabetes. With 1,004 nondiabetic individuals from the RISC study, we performed a genome-wide association study (GWAS) of 14 insulin sensitivity-related metabolites and one metabolite ratio. We replicated our results in the Botnia study (n = 342). We assessed the association of these variants with diabetes-related traits in GWAS meta-analyses (GENESIS [including RISC, EUGENE2, and Stanford], MAGIC, and DIAGRAM). We identified four associations with three metabolites-glycine (rs715 at CPS1), serine (rs478093 at PHGDH), and betaine (rs499368 at SLC6A12; rs17823642 at BHMT)-and one association signal with glycine-to-serine ratio (rs1107366 at ALDH1L1). There was no robust evidence for association between these variants and insulin resistance or diabetes. Genetic variants associated with genes in the glycine biosynthesis pathways do not provide consistent evidence for a role of glycine in diabetes-related traits.

Early metabolic markers of the development of dysglycemia and type 2 diabetes and their physiological significance

Metabolomic screening of fasting plasma from nondiabetic subjects identified α-hydroxybutyrate (α-HB) and linoleoyl-glycerophosphocholine (L-GPC) as joint markers of insulin resistance (IR) and glucose intolerance. To test the predictivity of α-HB and L-GPC for incident dysglycemia, α-HB and L-GPC measurements were obtained in two observational cohorts, comprising 1,261 nondiabetic participants from the Relationship between Insulin Sensitivity and Cardiovascular Disease (RISC) study and 2,580 from the Botnia Prospective Study, with 3-year and 9.5-year follow-up data, respectively. In both cohorts, α-HB was a positive correlate and L-GPC a negative correlate of insulin sensitivity, with α-HB reciprocally related to indices of β-cell function derived from the oral glucose tolerance test (OGTT). In follow-up, α-HB was a positive predictor (adjusted odds ratios 1.25 [95% CI 1.00-1.60] and 1.26 [1.07-1.48], respectively, for each standard deviation of predictor), and L-GPC was a negative predictor (0.64 [0.48-0.85] and 0.67 [0.54-0.84]) of dysglycemia (RISC) or type 2 diabetes (Botnia), independent of familial diabetes, sex, age, BMI, and fasting glucose. Corresponding areas under the receiver operating characteristic curve were 0.791 (RISC) and 0.783 (Botnia), similar in accuracy when substituting α-HB and L-GPC with 2-h OGTT glucose concentrations. When their activity was examined, α-HB inhibited and L-GPC stimulated glucose-induced insulin release in INS-1e cells. α-HB and L-GPC are independent predictors of worsening glucose tolerance, physiologically consistent with a joint signature of IR and β-cell dysfunction.

Perturbation of bile acid homeostasis is an early pathogenesis event of drug induced liver injury in rats

Drug-induced liver injury (DILI) is a significant consideration for drug development. Current preclinical DILI assessment relying on histopathology and clinical chemistry has limitations in sensitivity and discordance with human. To gain insights on DILI pathogenesis and identify potential biomarkers for improved DILI detection, we performed untargeted metabolomic analyses on rats treated with thirteen known hepatotoxins causing various types of DILI: necrosis (acetaminophen, bendazac, cyclosporine A, carbon tetrachloride, ethionine), cholestasis (methapyrilene and naphthylisothiocyanate), steatosis (tetracycline and ticlopidine), and idiosyncratic (carbamazepine, chlorzoxasone, flutamide, and nimesulide) at two doses and two time points. Statistical analysis and pathway mapping of the nearly 1900 metabolites profiled in the plasma, urine, and liver revealed diverse time and dose dependent metabolic cascades leading to DILI by the hepatotoxins. The most consistent change induced by the hepatotoxins, detectable even at the early time point/low dose, was the significant elevations of a panel of bile acids in the plasma and urine, suggesting that DILI impaired hepatic bile acid uptake from the circulation. Furthermore, bile acid amidation in the hepatocytes was altered depending on the severity of the hepatotoxin-induced oxidative stress. The alteration of the bile acids was most evident by the necrosis and cholestasis hepatotoxins, with more subtle effects by the steatosis and idiosyncratic hepatotoxins. Taking together, our data suggest that the perturbation of bile acid homeostasis is an early event of DILI. Upon further validation, selected bile acids in the circulation could be potentially used as sensitive and early DILI preclinical biomarkers.

A novel fasting blood test for insulin resistance and prediabetes

BACKGROUND

Insulin resistance (IR) can precede the dysglycemic states of prediabetes and type 2 diabetes mellitus (T2DM) by a number of years and is an early marker of risk for metabolic and cardiovascular disease. There is an unmet need for a simple method to measure IR that can be used for routine screening, prospective study, risk assessment, and therapeutic monitoring. We have reported several metabolites whose fasting plasma levels correlated with insulin sensitivity. These metabolites were used in the development of a novel test for IR and prediabetes.

METHODS

Data from the Relationship between Insulin Sensitivity and Cardiovascular Disease Study were used in an iterative process of algorithm development to define the best combination of metabolites for predicting the M value derived from the hyperinsulinemic euglycemic clamp, the gold standard measure of IR. Subjects were divided into a training set and a test set for algorithm development and validation. The resulting calculated M score, M(Q), was utilized to predict IR and the risk of progressing from normal glucose tolerance to impaired glucose tolerance (IGT) over a 3 year period.

RESULTS

M(Q) correlated with actual M values, with an r value of 0.66. In addition, the test detects IR and predicts 3 year IGT progression with areas under the curve of 0.79 and 0.70, respectively, outperforming other simple measures such as fasting insulin, fasting glucose, homeostatic model assessment of IR, or body mass index.

CONCLUSIONS

The result, Quantose(TM), is a simple test for IR based on a single fasting blood sample and may have value as an early indicator of risk for the development of prediabetes and T2DM.

Abstract 4541: Metabolomic diagnosis of prostate cancer from urine

There is a critical unmet need for new diagnostic tests to both determine if a patient has prostate cancer and whether that cancer is aggressive and therefore requires aggressive management. In this study we performed global metabolomic profiling on the post-DRE urine sediments of twenty-four men referred to the urologist with concern of prostate cancer. Eight of these men presented with benign prostatic conditions leading to a raised PSA while the remaining sixteen patients had clinical T3 prostate cancer. Global metabolomic profiling was carried out on methanolic extracts of these urine sediments. The resulting data sets were found to contain 256 metabolites based on spectral comparison against an in-house chemical reference library of over 2500 authentic standards. A subset of prostate cancer patients, but no patients with benign prostatic conditions, had elevated sarcosine abundance in their urine sediments. Patients with elevated sarcosine had a distinct metabolic signature that included sixty-five other differentially abundant metabolites, predominantly amino acids and their catabolites, differentiating these patients from the rest. The remaining prostate cancer patients could be differentiated from the patients with benign prostatic conditions based on their abundance profiles of acyl carnitines (increased) and uridine (reduced). Stable isotope dilution assays for select analytes confirmed these results, and several multianalyte algorithms were found to have good performance for the diagnosis of prostate cancer (AUROC &gt; 0.8). Both metabolic presentations of prostate cancer exhibited biochemical hallmarks of multiple acyl-coA dehydrogenase deficiency, an inborn error of metabolism that can be due to impaired activity of the mitochondrial electron transfer flavoprotein/quinone oxidase complex. These data indicate that post-DRE urine sediment profiling could provide valuable information regarding the need to refer the urologic patient for prostate biopsy and may hold additional insight into the molecular pathogenesis of prostate cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4541. doi:1538-7445.AM2012-4541

Abstract 4900: Development of a method for metabolomics and histology of tissue biopsies

Metabolomics, the global study of small molecules in a biological sample, is performed with the goal of extracting, identifying, and quantifying metabolites. As such, the technology is ideal for identifying biomarkers for diagnostics and drug therapy. One of the limitations with the current practice for metabolite extraction is that sample destruction precludes additional uses of the sample. This is particularly troublesome for high value samples with limited availability, such as clinical tumor biopsies. Clinical biopsies are taken in order to histologically diagnose and gauge cancer aggressiveness. Thus, physically disrupting these valuable samples is not ideal, even though quantitative metabolomic data could enhance histopathologic evaluation. In order to improve the amount of information obtained from patient biopsies, we have developed a method (termed PReservation by Extraction and Fixation, PREF) by which metabolite extraction simultaneously preserves the tissue for histological analysis. Briefly, upon sample collection, the biopsy is placed directly in methanol. Methanol incubation serves to recover metabolites, precipitate proteins, and fix the tissue. Following overnight incubation, the solvent is removed, evaporated to dryness, and reconstituted in a proprietary mixture of recovery standards. The needle biopsies are placed in biopsy bags and cassettes and transferred to Molecular Fixative until processed for histology. Solvent sample aliquots are taken for analysis on GC/MS and LC/MS platforms. Raw mass spectrometry data files are automatically extracted using a proprietary informatics system that includes peak identification and compound identification software. Compared to the current state of the art method for metabolite extraction, PREF recovers equivalent numbers and types of biochemicals from the tissue specimen. Furthermore, PREF preserves the tissue biopsy sample such that cellular architecture is retained, allowing for pathological analysis by chemical staining (hematoxylin & eosin) and antibody binding (immunohistochemistry). We have developed a non-destructive method for efficient metabolite extraction from tumor biopsies combined with preservation of the tissue for histological analysis. It is our hope that this novel method will augment the current histopathologic diagnosis and classification of tumors through quantitative measures of biochemicals in the same tissue. Given that certain biochemicals have been shown to correlate with disease aggressiveness, it is likely that this method will be valuable in helping to differentiate cancer aggressiveness.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4900. doi:10.1158/1538-7445.AM2011-4900

Ethylene glycol monomethyl ether-induced toxicity is mediated through the inhibition of flavoprotein dehydrogenase enzyme family

Ethylene glycol monomethyl ether (EGME) is a widely used industrial solvent known to cause adverse effects to human and other mammals. Organs with high metabolism and rapid cell division, such as testes, are especially sensitive to its actions. In order to gain mechanistic understanding of EGME-induced toxicity, an untargeted metabolomic analysis was performed in rats. Male rats were administrated with EGME at 30 and 100 mg/kg/day. At days 1, 4, and 14, serum, urine, liver, and testes were collected for analysis. Testicular injury was observed at day 14 of the 100 mg/kg/day group only. Nearly 1900 metabolites across the four matrices were profiled using liquid chromatography-mass spectrometry/mass spectrometry and gas chromatography-mass spectrometry. Statistical analysis indicated that the most significant metabolic perturbations initiated from the early time points by EGME were the inhibition of choline oxidation, branched-chain amino acid catabolism, and fatty acid β-oxidation pathways, leading to the accumulation of sarcosine, dimethylglycine, and various carnitine- and glycine-conjugated metabolites. Pathway mapping of these altered metabolites revealed that all the disrupted steps were catalyzed by enzymes in the primary flavoprotein dehydrogenase family, suggesting that inhibition of flavoprotein dehydrogenase-catalyzed reactions may represent the mode of action for EGME-induced toxicity. Similar urinary and serum metabolite signatures are known to be the hallmarks of multiple acyl-coenzyme A dehydrogenase deficiency in humans, a genetic disorder because of defects in primary flavoprotein dehydrogenase reactions. We postulate that disruption of key biochemical pathways utilizing flavoprotein dehydrogenases in conjugation with downstream metabolic perturbations collectively result in the EGME-induced tissue damage.

alpha-hydroxybutyrate is an early biomarker of insulin resistance and glucose intolerance in a nondiabetic population

BACKGROUND

Insulin resistance is a risk factor for type 2 diabetes and cardiovascular disease progression. Current diagnostic tests, such as glycemic indicators, have limitations in the early detection of insulin resistant individuals. We searched for novel biomarkers identifying these at-risk subjects.

METHODS

Using mass spectrometry, non-targeted biochemical profiling was conducted in a cohort of 399 nondiabetic subjects representing a broad spectrum of insulin sensitivity and glucose tolerance (based on the hyperinsulinemic euglycemic clamp and oral glucose tolerance testing, respectively).

RESULTS

Random forest statistical analysis selected alpha-hydroxybutyrate (alpha-HB) as the top-ranked biochemical for separating insulin resistant (lower third of the clamp-derived M(FFM) = 33 [12] micromol x min(-1) x kg(FFM) (-1), median [interquartile range], n = 140) from insulin sensitive subjects (M(FFM) = 66 [23] micromol x min(-1) x kg(FFM) (-1)) with a 76% accuracy. By targeted isotope dilution assay, plasma alpha-HB concentrations were reciprocally related to M(FFM); and by partition analysis, an alpha-HB value of 5 microg/ml was found to best separate insulin resistant from insulin sensitive subjects. alpha-HB also separated subjects with normal glucose tolerance from those with impaired fasting glycemia or impaired glucose tolerance independently of, and in an additive fashion to, insulin resistance. These associations were also independent of sex, age and BMI. Other metabolites from this global analysis that significantly correlated to insulin sensitivity included certain organic acid, amino acid, lysophospholipid, acylcarnitine and fatty acid species. Several metabolites are intermediates related to alpha-HB metabolism and biosynthesis.

CONCLUSIONS

alpha-hydroxybutyrate is an early marker for both insulin resistance and impaired glucose regulation. The underlying biochemical mechanisms may involve increased lipid oxidation and oxidative stress.

Biosynthesis of the sesquiterpene germacrene D in Solidago canadensis: 13C and (2)H labeling studies

The biogenetic origin of the isoprenoid building blocks of the sesquiterpene germacrene D was studied in Solidago canadensis. Feeding experiments were carried out with 1-[5,5-D(2)]deoxy-D-xylulose-5-phosphate (D(2)-DOXP), [5-13C]mevalonolactone (13C-MVL) and [1-13C]-D-glucose. The hydrodistillate of a cut shoot fed with D(2)-DOXP was investigated by enantio-MDGC-MS and the volatile fraction of a shoot supplied with 13C-MVL was examined by GC-C-IRMS. The incorporation of [1-13C]-D-glucose was analyzed by quantitative 13C NMR spectroscopy after isolation of germacrene D from the essential oil. Our labeling studies revealed that the biosynthesis of the C-15 skeleton of sesquiterpene germacrene D in Solidago canadensis proceeds predominantly via the methylerythritol phosphate pathway.

Biosynthesis of a hopane triterpene and three diterpenes in the liverwort Fossombronia alaskana

The biosynthesis of the triterpene 22-(30)-hopene-29-acid and the diterpenes 7,17-sacculatadiene-11,12-dial (sacculatal), trans-phytol and a new neoverrucosane-type diterpenoid (5-oxo-neoverrucos-(13)-ene) was studied by incorporation of [1-13C]-labelled glucose into axenic cultures of the artic liverwort Fossombronia alaskana. Quantitative 13C NMR spectroscopic analysis of the resulting labelling patterns showed that the isoprene units of the triterpene are derived from the mevalonic acid pathway, whereas the isoprene units of the diterpenes are built up via the methylerythritol phosphate pathway.

Biosynthesis of the hemi- and monoterpene moieties of isoprenyl phenyl ethers from the liverwort Trichocolea tomentella

The incorporation of 13C labelled glucose into trichocolein, deoxytomentellin, trans-phytol and stigmasterol has been studied in axenic cultures of the liverwort Trichocolea tomentella. Quantitative 13C NMR spectroscopic analysis of the resulting labelling patterns showed that the isoprene units of the hemi- and monoterpenoid moieties and the diterpene phytol are derived from the methylerythritol phosphate pathway, whereas the isoprene units of stigmasterol are built up via the mevalonic acid pathway. These results indicate the involvement of both IPP biosynthetic pathways in different cellular compartments. A new, hydroperoxy geranyl phenyl ether derivative is also described.

Biosynthesis of a neo-epi-verrucosane diterpene in the liverwort Fossombronia alaskana. A retrobiosynthetic NMR study

The biosynthesis of the diterpene 8alpha-acetoxy-13alpha-hydroxy-5-oxo-13-epi- neoverrucosane in the arctic liverwort Fossombronia alaskana was studied by incorporation experiments using [1-(13)C]- and [U-(13)C(6)]glucose as precursors. The (13)C-labeling patterns of acetyl-CoA, pyruvate, and phosphoenolpyruvate in intermediary metabolism were reconstructed from the (13)C NMR data of biosynthetic amino acids (leucine, alanine, phenylalanine) and were used to predict hypothetical labeling patterns for isopentenyl pyrophosphate formed via the mevalonate pathway and the deoxyxylulose pathway. The labeling patterns observed for the neoverrucosane diterpene were consistent with the intermediate formation of geranyllinaloyl pyrophosphate assembled from dimethylallyl pyrophosphate and three molecules of isopentenyl pyrophosphate generated predominantly or entirely via 1-deoxyxylulose 5-phosphate. The experimental data can be integrated into a detailed biosynthetic scheme involving a 1,5-hydride shift. The postulated involvement of the 1,5-hydride shift was confirmed by an incorporation experiment with [6,6-(2)H(2)]glucose.

Incorporation of 1-[1-(13)C]Deoxy-D-xylulose in chamomile sesquiterpenes

Incorporation of synthetically prepared 1-[1-(13)C]deoxy-d-xylulose into chamomile sesquiterpenes has been achieved by injecting an aqueous solution into the anthodia of the plant. The analysis of labeling patterns and absolute (13)C abundances of the isolated sesquiterpenes bisabololoxide A (1), bisabololoxide B (2), and chamazulene (3) using quantitative (13)C NMR spectroscopy showed that 1-[1-(13)C]deoxy-d-xylulose was efficiently incorporated in all three isoprene building blocks of the sesquiterpenes. A significantly lower (13)C abundance of the labeled carbon atom in the biogenetically terminal isoprene unit confirms the mixed biosynthesis of this unit, involving both the mevalonic acid pathway and the methylerythritol phosphate pathway.

Monoterpene biosynthesis in the liverwort Conocephalum conicum: demonstration of sabinene synthase and bornyl diphosphate synthase

(-)-Sabinene is the major monoterpene produced by a European strain of the liverwort Conocephalum conicum. A cell-free extract from in vitro cultured plants catalysed the cyclization of geranyl diphosphate to sabinene. The responsible monoterpene cyclase was partially purified and characterized as an operationally soluble enzyme of M(r) 65,000, with a pH optimum at 7.5 and a requirement for a divalent metal ion as the only cofactor, with Mg2+ preferred. The general properties of the sabinene synthase from C. conicum resemble those of other monoterpene cyclases from gymnosperms and angiosperms. A North American strain of the liverwort produces (+)-bornyl acetate as the major monoterpene and it was demonstrated that bornane-type monoterpenes are derived from geranyl diphosphate in this liverwort, as in higher plants, by the action of bornyl diphosphate synthase.

Involvement of the mevalonic acid pathway and the glyceraldehyde-pyruvate pathway in terpenoid biosynthesis of the liverworts Ricciocarpos natans and Conocephalum conicum

The incorporation of 13C-labeled glucose into borneol, bornyl acetate, the sesquiterpenes cubebanol and ricciocarpin A, phytol, and stigmasterol has been studied in axenic cultures of the liverworts Ricciocarpos natans and Conocephalum conicum. Quantitative 13C NMR spectroscopic analysis of the resulting labeling patterns showed that the isoprene building blocks of the sesquiterpenes and stigmasterol are built up via the mevalonic acid pathway, whereas the isoprene units of the monoterpenes and the diterpene phytol are exclusively derived from the glyceraldehyde-pyruvate pathway. These results indicate the involvement of both isopentenyl diphosphate biosynthetic pathways in different cellular compartments.

Partial purification and characterization of a monoterpene cyclase, limonene synthase, from the liverwort Ricciocarpos natans

4S-(-)-limonene is the major monoterpene accumulated by the liverwort Ricciocarpos natans, and a cell-free extract from this nonvascular plant cultured in vitro catalyzes the cyclization of geranyl diphosphate to limonene. The time course of limonene synthase activity parallels cultured growth but shows a maximum in specific activity in the lag phase following transfer to fresh medium. The operationally soluble enzyme was partially purified by combination of anion-exchange and hydroxylapatite chromatography. The limonene synthase from R. natans possesses a molecular weight of about 51,000, exhibits a pH optimum at 6.5, a pI at 5.3, and a requirement for either Mg2+ or Mn2+ as cofactor, and appears to employ 3S-linalyl disphosphate as a bound intermediate in the cyclization of the geranyl substrate (Km approximately 1.25 microM). In stereochemistry of the coupled isomerization-cyclization reaction and in general properties, the limonene synthase from this bryophyte resembles the corresponding monoterpene cyclases from gymnosperm and angiosperm species.

A lectin from the liverwort Marchantia polymorpha L

Bryophytes have been screened for lectins. From the liverwort Marchantia polymorpha (Marchiantiales) a lectin could be purified to homogeneity using a combination of ultrafiltration, size exclusion chromatography and ion exchange chromatography. SDS polyacrylamide gel electrophoresis, size exclusion chromatography and electrospray mass spectroscopy showed that the lectin is a monomeric protein with a M(r) of 16,134.64 +/- 2.93. Marchantia polymorpha lectin agglutinates erythrocytes of different mammalia and exhibits carbohydrate specificity against complex carbohydrate structures. This is the first report of a lectin isolated from liverworts.

Bisbibenzyl Formation in Aseptic Cultures of Marchantia polymorpha L

Three new aseptic cultures of Marchantia polymorpha from different collecting sites have been induced from the gametophytes. The formation of bisbibenzyls in differentiated cultures and cell suspension cultures was investigated. We observed that the production of the main bisbibenzyl, Marchantin A was induced by lack of nitrate and the addition of cupric sulfate to the medium. The comparison of bisbibenzyl patterns in three different cultures suggest the existence of chemical races of M. polymorpha. Bisbibenzyl patterns in differentiated cultures and cell suspension cultures appeared to be similar.