Chemical diversity in angiosperms - monoterpene synthases control complex reactions that provide the precursors for ecologically and commercially important monoterpenoids.

Monoterpene synthases (MTSs) catalyze the first committed step in the biosynthesis of monoterpenoids, a class of specialized metabolites with particularly high chemical diversity in angiosperms. In addition to accomplishing a rate enhancement, these enzymes manage the formation and turnover of highly reactive carbocation intermediates formed from a prenyl diphosphate substrate. At each step along the reaction path, a cationic intermediate can be subject to cyclization, migration of a proton, hydride, or alkyl group, or quenching to terminate the sequence. However, enzymatic control of ligand folding, stabilization of specific intermediates, and defined quenching chemistry can maintain the specificity for forming a signature product. This review article will discuss our current understanding of how angiosperm MTSs control the reaction environment. Such knowledge allows inferences about the origin and regulation of chemical diversity, which is pertinent for appreciating the role of monoterpenoids in plant ecology but also for aiding commercial efforts that harness the accumulation of these specialized metabolites for the food, cosmetic, and pharmaceutical industries.

Differential Accumulation of Metabolites and Transcripts Related to Flavonoid, Styrylpyrone, and Galactolipid Biosynthesis in Equisetum Species and Tissue Types.

Three species of the genus Equisetum (E. arvense, E. hyemale, and E. telmateia) were selected for an analysis of chemical diversity in an ancient land plant lineage. Principal component analysis of metabolomics data obtained with above-ground shoot and below-ground rhizome extracts enabled a separation of all sample types, indicating species- and organ-specific patterns of metabolite accumulation. Follow-up efforts indicated that galactolipids, carotenoids, and flavonoid glycosides contributed positively to the separation of shoot samples, while stryrylpyrone glycosides and phenolic glycosides were the most prominent positive contributors to the separation of rhizome samples. Consistent with metabolite data, genes coding for enzymes of flavonoid and galactolipid biosynthesis were found to be expressed at elevated levels in shoot samples, whereas a putative styrylpyrone synthase gene was expressed preferentially in rhizomes. The current study builds a foundation for future endeavors to further interrogate the organ and tissue specificity of metabolism in the last living genus of a fern family that was prevalent in the forests of the late Paleozoic era.

Flavonoid deficiency disrupts redox homeostasis and terpenoid biosynthesis in glandular trichomes of tomato.

Glandular trichomes (GTs) are epidermal structures that provide the first line of chemical defense against arthropod herbivores and other biotic threats. The most conspicuous structure on leaves of cultivated tomato (Solanum lycopersicum) is the type-VI GT (tVI-GT), which accumulates both flavonoids and volatile terpenoids. Although these classes of specialized metabolites are derived from distinct metabolic pathways, previous studies with a chalcone isomerase 1 (CHI1)-deficient mutant called anthocyanin free (af) showed that flavonoids are required for terpenoid accumulation in tVI-GTs. Here, we combined global transcriptomic and proteomic analyses of isolated trichomes as a starting point to show that the lack of CHI1 is associated with reduced levels of terpenoid biosynthetic transcripts and enzymes. The flavonoid deficiency in af trichomes also resulted in the upregulation of abiotic stress-responsive genes associated with DNA damage and repair. Several lines of biochemical and genetic evidence indicate that the terpenoid defect in af mutants is specific for the tVI-GT and is associated with the absence of bulk flavonoids rather than loss of CHI1 per se. A newly developed genome-scale model of metabolism in tomato tVI-GTs helped identify metabolic imbalances caused by the loss of flavonoid production. We provide evidence that flavonoid deficiency in this cell type leads to increased production of reactive oxygen species (ROS), which may impair terpenoid biosynthesis. Collectively, our findings support a role for flavonoids as ROS-scavenging antioxidants in GTs.

Genome-Wide Analysis of Terpene Synthase Gene Family in Mentha longifolia and Catalytic Activity Analysis of a Single Terpene Synthase.

Terpenoids are a wide variety of natural products and terpene synthase (TPS) plays a key role in the biosynthesis of terpenoids. Mentha plants are rich in essential oils, whose main components are terpenoids, and their biosynthetic pathways have been basically elucidated. However, there is a lack of systematic identification and study of TPS in Mentha plants. In this work, we genome-widely identified and analyzed the TPS gene family in Mentha longifolia, a model plant for functional genomic research in the genus Mentha. A total of 63 TPS genes were identified in the M. longifolia genome sequence assembly, which could be divided into six subfamilies. The TPS-b subfamily had the largest number of genes, which might be related to the abundant monoterpenoids in Mentha plants. The TPS-e subfamily had 18 members and showed a significant species-specific expansion compared with other sequenced Lamiaceae plant species. The 63 TPS genes could be mapped to nine scaffolds of the M. longifolia genome sequence assembly and the distribution of these genes is uneven. Tandem duplicates and fragment duplicates contributed greatly to the increase in the number of TPS genes in M. longifolia. The conserved motifs (RR(X)8W, NSE/DTE, RXR, and DDXXD) were analyzed in M. longifolia TPSs, and significant differentiation was found between different subfamilies. Adaptive evolution analysis showed that M. longifolia TPSs were subjected to purifying selection after the species-specific expansion, and some amino acid residues under positive selection were identified. Furthermore, we also cloned and analyzed the catalytic activity of a single terpene synthase, MlongTPS29, which belongs to the TPS-b subfamily. MlongTPS29 could encode a limonene synthase and catalyze the biosynthesis of limonene, an important precursor of essential oils from the genus Mentha. This study provides useful information for the biosynthesis of terpenoids in the genus Mentha.

Correction: Chen et al. Genome-Wide Analysis of Terpene Synthase Gene Family in Mentha longifolia and Catalytic Activity Analysis of a Single Terpene Synthase. Genes 2021, 12, 518.

The authors have requested that the following changes be made to their paper [...].

Biochemical characterization of acyl activating enzymes for side chain moieties of Taxol and its analogs.

Taxol (paclitaxel) is a very widely used anticancer drug, but its commercial sources mainly consist of stripped bark or suspension cultures of members of the plant genus Taxus. Taxol accumulates as part of a complex mixture of chemical analogs, termed taxoids, which complicates its production in pure form, highlighting the need for metabolic engineering approaches for high-level Taxol production in cell cultures or microbial hosts. Here, we report on the characterization of acyl-activating enzymes (AAEs) that catalyze the formation of CoA esters of different organic acids relevant for the N-substitution of the 3-phenylisoserine side chain of taxoids. On the basis of similarities to AAE genes of known function from other organisms, we identified candidate genes in publicly available transcriptome data sets obtained with Taxus × media. We cloned 17 AAE genes, expressed them heterologously in Escherichia coli, purified the corresponding recombinant enzymes, and performed in vitro assays with 27 organic acids as potential substrates. We identified TmAAE1 and TmAAE5 as the most efficient enzymes for the activation of butyric acid (Taxol D side chain), TmAAE13 as the best candidate for generating a CoA ester of tiglic acid (Taxol B side chain), TmAAE3 and TmAAE13 as suitable for the activation of 4-methylbutyric acid (N-debenzoyl-N-(2-methylbutyryl)taxol side chain), TmAAE15 as a highly efficient candidate for hexanoic acid activation (Taxol C side chain), and TmAAE4 as suitable candidate for esterification of benzoic acid with CoA (Taxol side chain). This study lays important groundwork for metabolic engineering efforts aimed at improving Taxol production in cell cultures.

Enzymology of monoterpene functionalization in glandular trichomes.

The plant kingdom supports an extraordinary chemical diversity, with terpenoids representing a particularly diversified class of secondary (or specialized) metabolites. Volatile and semi-volatile terpenoids in the C10-C20 range are often formed in specialized cell types and secretory structures. In the angiosperm lineage, glandular trichomes play an important role in enabling the biosynthesis and storage (or in some cases secretion) of functionalized terpenoids. The 'decoration' of a terpenoid scaffold with functional groups changes its physical and chemical properties, and can therefore affect the perception of a specific metabolite by other organisms. Because of the ecological implications (e.g. plant-herbivore interactions) and commercial relevance (e.g. volatiles used in the flavor and fragrance industries), terpenoid functionalization has been researched extensively. Recent successes in the cloning and functional evaluation of genes as well as the structural and biochemical characterization of enzyme catalysts have laid the foundation for an improved understanding of how pathways toward functionalized monoterpenes may have evolved. In this review, we will focus on an up-to-date account of functionalization reactions present in glandular trichomes.

Efficacy and safety of tapentadol prolonged release formulation in the treatment of elderly patients with moderate-to-severe chronic osteoarthritis knee pain: a pooled analysis of two double-blind, randomized, placebo-, and active-controlled trials.

OBJECTIVE: To compare efficacy and safety of tapentadol prolonged release (PR) vs oxycodone controlled release (CR) in younger patients (<65 years of age) and in elderly patients (≥65 and ≥75 years of age) in the treatment of moderate-to-severe chronic osteoarthritis (OA) knee pain. METHODS: Data from two double-blind, randomized, placebo-, and oxycodone CR-controlled phase 3 trials were pooled and stratified by age. Primary efficacy end-points were change from baseline in average pain intensity at week 12 (US end-point) and over the entire maintenance period (non-US end-point). RESULTS: A total of 1357 patients <65 years, 653 patients ≥65 years, and 176 patients ≥75 years of age were assessed. The comparison between tapentadol PR and oxycodone CR showed numerically better pain relief under tapentadol PR for both primary end-points in all three age groups. More favorable improvements were also observed for patient global impression of change, the Short Form-36 physical component score, and EuroQoL-5Dimensions health status index. In the elderly, incidences of dizziness and somnolence were comparable between active treatments, but incidences of nausea, vomiting, and constipation were considerably lower under tapentadol PR. Treatment completion rates were lowest under oxycodone CR; > 50% of elderly oxycodone CR patients named side-effects as the main reason for discontinuation. CONCLUSIONS: Tapentadol PR was effective in the treatment of moderate-to-severe chronic OA pain in elderly and younger patients. Compared to oxycodone CR, the overall and the gastrointestinal tolerability profile in particular were better in all tapentadol PR groups, regardless of age.

Comparison of the Legiolert™/Quanti-Tray® MPN test for the enumeration of Legionella pneumophila from potable water samples with the German regulatory requirements methods ISO 11731-2 and ISO 11731.

Due to the promising results of a previous study of the performance of the novel MPN method (Legiolert™/Quanti-Tray®) compared to ISO 11731-2, this study was performed to compare Legiolert for Legionella pneumophila with the German regulatory requirements methods ISO 11731-2 (100 ml membrane filtration) and ISO 11731 (1 ml direct plating) for the enumeration of L. pneumophila and Legionella spp. from potable water. Data from a multi-laboratory study according to ISO 17994 showed that Legiolert yielded on average higher counts of L. pneumophila than the ISO 11731-2 method, but the comparison with ISO 11731 was inconclusive due to the number of samples needing to be tested. Likewise, comparisons of the MPN method for 100 ml to the highest result of either ISO 11731 or ISO 11731-2 according to Federal Environmental Agency recommendation (2012) yielded no conclusive difference, regardless of whether non-pneumophila species of Legionella were included in the evaluation. The MPN method has a high specificity for L. pneumophila of 97.9% which compares favourably to the specificity of 95.3% quoted for ISO 11731. The new method represents a significant improvement in the enumeration of L. pneumophila from drinking water and related samples.

Coenzyme M biosynthesis in bacteria involves phosphate elimination by a functionally distinct member of the aspartase/fumarase superfamily.

For nearly 30 years, coenzyme M (CoM) was assumed to be present solely in methanogenic archaea. In the late 1990s, CoM was reported to play a role in bacterial propene metabolism, but no biosynthetic pathway for CoM has yet been identified in bacteria. Here, using bioinformatics and proteomic approaches in the metabolically versatile bacterium Xanthobacter autotrophicus Py2, we identified four putative CoM biosynthetic enzymes encoded by the xcbB1, C1, D1, and E1 genes. Only XcbB1 was homologous to a known CoM biosynthetic enzyme (ComA), indicating that CoM biosynthesis in bacteria involves enzymes different from those in archaea. We verified that the ComA homolog produces phosphosulfolactate from phosphoenolpyruvate (PEP), demonstrating that bacterial CoM biosynthesis is initiated similarly as the phosphoenolpyruvate-dependent methanogenic archaeal pathway. The bioinformatics analysis revealed that XcbC1 and D1 are members of the aspartase/fumarase superfamily (AFS) and that XcbE1 is a pyridoxal 5'-phosphate-containing enzyme with homology to d-cysteine desulfhydrases. Known AFS members catalyze ß-elimination reactions of succinyl-containing substrates, yielding fumarate as the common unsaturated elimination product. Unexpectedly, we found that XcbC1 catalyzes ß-elimination on phosphosulfolactate, yielding inorganic phosphate and a novel metabolite, sulfoacrylic acid. Phosphate-releasing ß-elimination reactions are unprecedented among the AFS, indicating that XcbC1 is an unusual phosphatase. Direct demonstration of phosphosulfolactate synthase activity for XcbB1 and phosphate ß-elimination activity for XcbC1 strengthened their hypothetical assignment to a CoM biosynthetic pathway and suggested functions also for XcbD1 and E1. Our results represent a critical first step toward elucidating the CoM pathway in bacteria.

Tapentadol prolonged-release for moderate-to-severe chronic osteoarthritis knee pain: a double-blind, randomized, placebo- and oxycodone controlled release-controlled study.

OBJECTIVE: To assess efficacy and safety of tapentadol prolonged release (PR) for moderate-to-severe chronic osteoarthritis knee pain. METHODS: Patients (n = 990) were randomized (1:1:1) to tapentadol PR, oxycodone controlled release (CR; reference compound for assay sensitivity), or placebo for a double-blind 3-week titration and 12-week maintenance period. Primary efficacy end-points were change from baseline in average pain intensity at week 12 of maintenance (US end-point) and over the entire maintenance period (non-US end-point) with "last observation carried forward" as imputation method for missing scores. RESULTS: Both primary end-points were not significantly different for tapentadol PR nor for oxycodone CR vs placebo at week 12 (least squares [LS] mean difference = -0.3 [95% CI = -0.61-0.09]; p = 0.152 and 0.2 [95% CI = -0.16-0.54]; p = 0.279, respectively) and over the maintenance period (LS mean difference = -0.2 [95% CI = -0.55-0.07]; p = 0.135 and 0.1 [95% CI = -0.18-0.44]; p = 0.421, respectively). Considerably more patients receiving tapentadol PR than oxycodone CR completed the trial (58.3% vs 36.6%). This is consistent with better results with tapentadol PR on the overall health status (PGIC) compared to oxycodone CR. Indeed, respectively, 56% and 42.5% rated at least "much improved" at the end of treatment. Incidences of gastrointestinal adverse events were higher for both active treatments compared to placebo. Tapentadol PR was associated with a better gastrointestinal tolerability profile with incidences of constipation (17.9% vs 35%) and of the composite of nausea and/or vomiting (23.8% vs 46.8%) significantly lower vs oxycodone CR (p < 0.001). CONCLUSIONS: The study did not demonstrate assay sensitivity. The finding that both primary end-points for tapentadol PR were not met can, thus, not be interpreted. Tapentadol PR was better tolerated than oxycodone CR, largely due to fewer gastrointestinal side-effects.

Efficacy and safety of tapentadol prolonged release for moderate-to-severe chronic osteoarthritis knee pain: a pooled analysis of two double-blind, randomized, placebo- and oxycodone controlled release-controlled studies.

OBJECTIVE: To compare efficacy and safety of tapentadol prolonged-release (PR) and oxycodone-controlled release (CR) in moderate-to-severe chronic osteoarthritis knee pain. METHODS: Data from two double-blind, randomized, placebo- and oxycodone CR-controlled phase 3 studies with a 3-week titration period and 12-week controlled dose adjustment maintenance period were pooled. Primary efficacy end-points were change from baseline in average pain intensity at week 12 (US end-point) and over the entire maintenance period (non-US end-point). RESULTS: A total of 2,010 patients were assessed. For both primary end-points, tapentadol PR was significantly more effective than oxycodone CR (LS mean difference of -0.41 [95% CI = -0.65, -0.16; p = 0.001] at week 12 and -0.35 [95% CI = -0.58, -0.12; p = 0.003] over 12 weeks of maintenance [last observation carried forward]). Significantly better outcomes than for oxycodone CR were also observed for patient global impression of change, both Short Form-36 component scores, and EuroQoL-5Dimensions health status index (all p < 0.001). Relative risk for vomiting, constipation, nausea, somnolence, and pruritus was lower for tapentadol PR than for oxycodone CR. A higher proportion of oxycodone CR patients discontinued treatment (64% vs 42.2% for tapentadol PR); time to treatment discontinuation due to an adverse event was significantly shorter for oxycodone CR (p < 0.001). CONCLUSIONS: The analyses suggest that tapentadol PR provided superior pain relief and a more improved overall health status than oxycodone CR in a large patient population with moderate-to-severe chronic osteoarthritis pain. Compared to oxycodone CR, tapentadol PR showed a more favorable tolerability profile with better gastrointestinal tolerability.

Comprehensive Assessment of Transcriptional Regulation Facilitates Metabolic Engineering of Isoprenoid Accumulation in Arabidopsis.

In plants, two spatially separated pathways provide the precursors for isoprenoid biosynthesis. We generated transgenic Arabidopsis (Arabidopsis thaliana) lines with modulated levels of expression of each individual gene involved in the cytosolic/peroxisomal mevalonate and plastidial methylerythritol phosphate pathways. By assessing the correlation of transgene expression levels with isoprenoid marker metabolites (gene-to-metabolite correlation), we determined the relative importance of transcriptional control at each individual step of isoprenoid precursor biosynthesis. The accumulation patterns of metabolic intermediates (metabolite-to-gene correlation) were then used to infer flux bottlenecks in the sterol pathway. The extent of metabolic cross talk, the exchange of isoprenoid intermediates between compartmentalized pathways, was assessed by a combination of gene-to-metabolite and metabolite-to-metabolite correlation analyses. This strategy allowed the selection of genes to be modulated by metabolic engineering, and we demonstrate that the overexpression of predictable combinations of genes can be used to significantly enhance flux toward specific end products of the sterol pathway. Transgenic plants accumulating increased amounts of sterols are characterized by significantly elevated biomass, which can be a desirable trait in crop and biofuel plants.

Predictors of the placebo analgesia response in randomized controlled trials of chronic pain: a meta-analysis of the individual data from nine industrially sponsored trials.

A large number of analgesics have failed to prove superiority over placebo in randomized controlled trials (RCTs), and as this has been related to increasing placebo responses, there is currently an interest in specifying predictors of the placebo response. The literature on placebo mechanisms suggests that factors related to patients' expectations of treatment efficacy are pivotal for the placebo response. Also, general characteristics of RCTs have been suggested to influence the placebo response. Yet, only few meta-analyses have directly tested these hypotheses. Placebo data from 9 industrially sponsored, randomized, double-blind, placebo-controlled, multicenter phase III trials in 2017 adult patients suffering from chronic painful osteoarthritis (hip or knee) or low back pain were included. The primary outcome was pain intensity. Based on previous studies, we chose 3 expectancy-related primary predictors: type of active medication, randomization ratio, and number of planned face-to-face visits. In addition, explorative analyses tested whether RCT and patients' characteristics predicted the placebo response. Opioid trials, a high number of planned face-to-face visits, and randomization ratio predicted the magnitude of the placebo response, thereby supporting the expectancy hypothesis. Exploratory models with baseline pain intensity, age, washout length, and discontinuation because of adverse events accounted for approximately 10% of the variability in the placebo response. Based on these results and previous mechanisms studies, we think that patients' perception of treatment allocation and expectations toward treatment efficacy could potently predict outcomes of RCTs.

Open-access metabolomics databases for natural product research: present capabilities and future potential.

Various databases have been developed to aid in assigning structures to spectral peaks observed in metabolomics experiments. In this review article, we discuss the utility of currently available open-access spectral and chemical databases for natural products discovery. We also provide recommendations on how the research community can contribute to further improvements.

Patterns of metabolite changes identified from large-scale gene perturbations in Arabidopsis using a genome-scale metabolic network.

Metabolomics enables quantitative evaluation of metabolic changes caused by genetic or environmental perturbations. However, little is known about how perturbing a single gene changes the metabolic system as a whole and which network and functional properties are involved in this response. To answer this question, we investigated the metabolite profiles from 136 mutants with single gene perturbations of functionally diverse Arabidopsis (Arabidopsis thaliana) genes. Fewer than 10 metabolites were changed significantly relative to the wild type in most of the mutants, indicating that the metabolic network was robust to perturbations of single metabolic genes. These changed metabolites were closer to each other in a genome-scale metabolic network than expected by chance, supporting the notion that the genetic perturbations changed the network more locally than globally. Surprisingly, the changed metabolites were close to the perturbed reactions in only 30% of the mutants of the well-characterized genes. To determine the factors that contributed to the distance between the observed metabolic changes and the perturbation site in the network, we examined nine network and functional properties of the perturbed genes. Only the isozyme number affected the distance between the perturbed reactions and changed metabolites. This study revealed patterns of metabolic changes from large-scale gene perturbations and relationships between characteristics of the perturbed genes and metabolic changes.

The evolution of plant secretory structures and emergence of terpenoid chemical diversity.

Secretory structures in terrestrial plants appear to have first emerged as intracellular oil bodies in liverworts. In vascular plants, internal secretory structures, such as resin ducts and laticifers, are usually found in conjunction with vascular bundles, whereas subepidermal secretory cavities and epidermal glandular trichomes generally have more complex tissue distribution patterns. The primary function of plant secretory structures is related to defense responses, both constitutive and induced, against herbivores and pathogens. The ability to sequester secondary (or specialized) metabolites and defense proteins in secretory structures was a critical adaptation that shaped plant-herbivore and plant-pathogen interactions. Although this review places particular emphasis on describing the evolution of pathways leading to terpenoids, it also assesses the emergence of other metabolite classes to outline the metabolic capabilities of different plant lineages.

Biosynthesis and Biotechnology of High-Value p-Menthane Monoterpenes, Including Menthol, Carvone, and Limonene.

Monoterpenes of the p-menthane group are volatile secondary (or specialized) metabolites found across the plant kingdom. They are dominant constituents of commercially important essential oils obtained from members of the genera Mentha (Lamiaceae), Carum (Apiaceae), Citrus (Rutaceae), and Eucalyptus (Myrtaceae). p-Menthane monoterpenes have also attracted interest as chiral specialty chemicals, and the harvest from natural sources is therefore supplemented by chemical synthesis. More recently, microbial and plant-based platforms for the high-level accumulation of specific target monoterpenes have been developed. In this review chapter, I discuss the properties of the genes and enzymes involved in p-menthane biosynthesis and provide a critical assessment of biotechnological production approaches.

A pooled analysis evaluating the efficacy and tolerability of tapentadol extended release for chronic, painful diabetic peripheral neuropathy.

BACKGROUND AND OBJECTIVE: Data from two similarly designed studies of tapentadol extended release (ER) for managing neuropathic pain associated with diabetic peripheral neuropathy (DPN; NCT00455520, NCT01041859) in adults were pooled for this analysis, allowing a detailed evaluation of efficacy in patient subgroups and secondary endpoints. METHODS: In each study, patients were titrated to their optimal dose of open-label tapentadol ER [100-250 mg twice daily (bid)] over 3 weeks. Patients with ≥1-point improvement in average pain intensity [11-point numerical rating scale (NRS)] were randomized (1:1) to receive placebo or tapentadol ER during a 12-week, double-blind maintenance period. RESULTS: Mean (standard deviation [SD]) changes in pain intensity from baseline to week 12 of maintenance in the placebo (n = 343) and tapentadol ER (n = 360) groups, respectively, were 1.28 (2.41) and 0.08 (1.87) [least squares mean difference (LSMD): -1.14 (95 % confidence interval [CI]: -1.435, -0.838); P < 0.001, in favour of tapentadol ER]. Significant between-group differences were also observed in changes from the start of the double-blind treatment period to the double-blind endpoint for the Short Form-36 physical functioning, role-physical, bodily pain, social functioning and role-emotional subscale and physical component summary scores, and the EuroQol 5-Dimension health status index (all P < 0.05, in favour of tapentadol ER). No clinically relevant differences were observed in the efficacy of tapentadol ER across patient subgroups divided by age, sex, race, opioid experience and pain intensity. Incidences of treatment-emergent adverse events were 56.0 % (192/343) with placebo and 74.7 % (269/360) with tapentadol ER during maintenance. CONCLUSION: Results of this pooled analysis indicate that tapentadol ER was effective for managing DPN-related pain, and provided consistent analgesic efficacy across different patient subgroups.