Quinolizidine and Pyrrolizidine Alkaloid Chemical Ecology – a Mini-Review on Their Similarities and Differences

The fate of quinolizidine alkaloids during the processing of lupins (Lupinus spp.) for human consumption

Lupin, a protein-rich grain legume, and products thereof, are becoming increasingly important in our diets. However, variable and high concentrations of quinolizidine alkaloids (QAs) may hamper this evolution. This study assessed the fate of QAs when processing Lupinus albus seeds and lupin-based foods, to give a first indication of the food industry's ability to sufficiently reduce the QA concentration. Typical unit processes, including toasting, dehulling, sterilization (sterilized jarred lupins), oven baking (cookies), frying (chips) and boiling in water (pasta), were simulated on lab-scale. A quantitative determination of five QAs and qualitative screening of other relevant QAs, in the derived fractions and lupin-based foods, was performed with a validated UHPLC-MS/MS and -HRMS method, respectively. Results revealed that the reduction in quinolizidine alkaloid content is highly dependent on the applied unit process, that QAs appear to be heat stabile, and that the depletion can be attributed to the leaching in cooking water.

Upcycling post-harvest biomass residues from native European Lupinus species: from straws and pod shells production to nutritive value and alkaloids content for ruminant animals

The production of Lupinus seeds for food and feed is increasing worldwide, which results in large amounts of post-harvest biomass residues, considered of low value and left in the field to be burned or incorporated in the soil. To valorize these agricultural wastes, this work aimed to assess their potential as an alternative feed for ruminants. Thus, the production yield, nutritive value, and alkaloid content of straws and pod shells from three native European Lupinus species, L. albus 'Estoril' (white), L. angustifolius 'Tango' (narrow-leafed), and L. luteus 'Cardiga' (yellow), cultivated in two locations, were evaluated. The dry matter (DM) yield of straws and pod shells were the highest for L. albus 'Estoril' (4.10 t ha^-1) and the lowest for L. angustifolius 'Tango' (1.78 t ha^-1), suggesting a poor adaptation of narrow-leafed lupin to the particularly dry and warm agronomic year. Despite species-specific differences, lupin biomass residues presented higher crude protein (53.0-68.9 g kg^-1 DM) and lignin (103-111 g kg^-1 DM) content than cereal straws usually used in ruminant feeding, thus resulting in higher metabolizable energy (6.43-6.58 MJ kg^-1 DM) content. In vitro digestibility was similar among lupin species (47.7-50.6%) and higher in pod shells (53.7%) than in straws (44.6%). Lupinus albus 'Estoril' and L. luteus 'Cardiga' presented considerable amounts of alkaloids in straws (23.9 and 119 mg kg^-1 DM) and pod shells (20.5 and 298 mg kg^-1 DM), while no alkaloids were detected in L. angustifolius 'Tango' biomass residues. Considering the combined production of straw and pod shells per lupin species, it is anticipated that lupin biomass residues produced per ha can fulfill 85% of the energy and nearly 50% of protein requirements of a flock of 4 to 9 dry and mid-pregnancy sheep with 50 kg body weight for one year. No negative effects on small (ovine) and large (bovine) ruminant species due to alkaloids are expected, even if biomass residues are consumed at up to 85% DM intake. The large production yield along with its nutritive value unveils the potential of lupin biomass residues valorization as alternative fodder for ruminants, promoting sustainability under a circular economy approach.

Metabolic pathway genes for editing to enhance multiple disease resistance in plants

Diseases are one of the major constraints in commercial crop production. Genetic diversity in varieties is the best option to manage diseases. Molecular marker-assisted breeding has produced hundreds of varieties with good yields, but the resistance level is not satisfactory. With the advent of whole genome sequencing, genome editing is emerging as an excellent option to improve the inadequate traits in these varieties. Plants produce thousands of antimicrobial secondary metabolites, which as polymers and conjugates are deposited to reinforce the secondary cell walls to contain the pathogen to an initial infection area. The resistance metabolites or the structures produced from them by plants are either constitutive (CR) or induced (IR), following pathogen invasion. The production of each resistance metabolite is controlled by a network of biosynthetic R genes, which are regulated by a hierarchy of R genes. A commercial variety also has most of these R genes, as in resistant, but a few may be mutated (SNPs/InDels). A few mutated genes, in one or more metabolic pathways, depending on the host-pathogen interaction, can be edited, and stacked to increase resistance metabolites or structures produced by them, to achieve required levels of multiple pathogen resistance under field conditions.

Investigations on the Transfer of Quinolizidine Alkaloids from Lupinus angustifolius into the Milk of Dairy Cows

Lupin varieties with a low content of quinolizidine alkaloids (QAs) like blue sweet lupin (BSL) have long been used as a protein source for dairy cows. A health concern for humans may arise from the transfer of acute toxic QAs from feed into cow's milk. This study is the first to quantify the transfer of QAs from BSL into cow's milk with experimental and modeling methods. Four lactating dairy cows were subjected to two 7 day feeding periods with 1 and 2 kg/d BSL, respectively, each followed by a depuration period. BSL contained 1774 mg/kg dry matter total QAs. Individual milk samples were taken twice daily and QA contents in feed and milk determined with liquid chromatography-tandem mass spectrometry. Transfer of QAs into the milk was already seen with the administration of 1 kg/d BSL, with differences in transfer rates (TRs) between individual QAs. A toxicokinetic model was derived to quantify and predict QA feed-to-food transfer. For the four most prominent QAs, our model shows an α-half-life of around 0.27 d. TRs were obtained for six QAs and were between 0.13 (sparteine) and 3.74% (multiflorine). A toxicological assessment of milk containing QAs as measured in this study indicated a potential health concern.

What Goes in Must Come Out? The Metabolic Profile of Plants and Caterpillars, Frass, And Adults of Asota (Erebidae: Aganainae) Feeding on Ficus (Moraceae) in New Guinea

Insect herbivores have evolved a broad spectrum of adaptations in response to the diversity of chemical defences employed by plants. Here we focus on two species of New Guinean Asota and determine how these specialist moths deal with the leaf alkaloids of their fig (Ficus) hosts. As each focal Asota species is restricted to one of three chemically distinct species of Ficus, we also test whether these specialized interactions lead to similar alkaloid profiles in both Asota species. We reared Asota caterpillars on their respective Ficus hosts in natural conditions and analyzed the alkaloid profiles of leaf, frass, caterpillar, and adult moth samples using UHPLC-MS/MS analyses. We identified 43 alkaloids in our samples. Leaf alkaloids showed various fates. Some were excreted in frass or found in caterpillars and adult moths. We also found two apparently novel indole alkaloids-likely synthesized de novo by the moths or their microbiota-in both caterpillar and adult tissue but not in leaves or frass. Overall, alkaloids unique or largely restricted to insect tissue were shared across moth species despite feeding on different hosts. This indicates that a limited number of plant compounds have a direct ecological function that is conserved among the studied species. Our results provide evidence for the importance of phytochemistry and metabolic strategies in the formation of plant-insect interactions and food webs in general. Furthermore, we provide a new potential example of insects acquiring chemicals for their benefit in an ecologically relevant insect genus.

Indole and quinolizidine alkaloids from blue lupin leach to agricultural drainage water

Phytotoxins are produced in plants including agricultural crops. Lupins and other plants of the Fabaceae family produce toxic alkaloids. These alkaloids have been studied in food and feed, however, the environmental fate of alkaloids produced by cultivated lupins is largely unknown. Therefore, we conducted an agricultural field experiment to investigate the occurrence of indole and quinolizidine alkaloids in lupin plant tissues, soil, soil pore water and in drainage water. During the field experiment, alkaloids were regularly quantified (median concentrations) in lupin (13-8.7 × 10³ ng/g dry weight (dw)), and topsoils at depth 0-5 cm (0.1-10 ng/g dw), and depth 15-30 cm (0.2-8.5 ng/g dw), soil pore water (0.2-7.5 ng/L) and drainage water samples (0.4-18 ng/L). Lupanine was the dominant alkaloid in all collected samples. Cumulative amounts of alkaloids emitted via drainage water were around 0.1-11 mg/ha for individual alkaloids over one growing season. The total cumulative amount of alkaloid in drainage water was 14 mg/ha, which is a very small amount compared to the mass of alkaloid in the lupin biomass (11 kg/ha) and soil (0.02 kg/ha). Nearly half of the alkaloids were exported in the drainage water during high flow events, indicating that alkaloids transport preferentially via macropores. These findings indicate that drainage from lupin cultivated areas contribute to surface water contamination. The environmental and ecotoxicological relevance of alkaloids as newly identified aquatic micropollutants in areas with agricultural activities have yet to be assessed.

Current Understanding of Modes of Action of Multicomponent Bioactive Phytochemicals: Potential for Nutraceuticals and Antimicrobials

Plants produce a diversity of plant secondary metabolites (PSMs), which function as defense chemicals against herbivores and microorganisms but also as signal compounds. An individual plant produces and accumulates mixtures of PSMs with different structural features using different biosynthetic pathways. Almost all PSMs exert one or several biological activities that can be useful for nutrition and health. This review discusses the modes of action of PSMs alone and in combinations. In a mixture, most individual PSMs can modulate different molecular targets; they are thus multitarget drugs. In an extract with many multitarget chemicals, additive and synergistic effects occur. Experiments with the model system Caenorhabditis elegans show that polyphenols and carotenoids can function as powerful antioxidative and longevity-promoting PSMs. PSMs of food plants and spices often exhibit antioxidant, anti-inflammatory, and antimicrobial properties, which can be beneficial for health and the prevention of diseases. Some extracts from food plants and spices with bioactive PSMs have potential for nutraceuticals and antimicrobials.

Introduced populations of the garden lupine are adapted to local generalist snails but have lost alkaloid diversity

Intraspecific variation in growth and defence among plant populations can be driven by differences in (a)biotic conditions, such as herbivory and resources. Introduction of species to novel environments affects simultaneously herbivory encountered by a plant and resource availability both directly and via altered competitive environment. Here, we address the question of how growth (leaf mass per area (LMA), plant size) and resistance traits (leaf alkaloids, leaf trichomes, resistance to a generalist snail) vary and covary between native and introduced populations of the garden lupine, Lupinus polyphyllus. We focused specifically on evolved differences among populations by measuring traits from plants grown from seed in a common environment. Plants from the introduced populations were more resistant against the generalist snail, Arianta arbustorum, and they had more leaf trichomes and higher LMA than plants from the native populations. The composition of alkaloids differed between native and introduced populations, with the native populations having more diversity in alkaloids among them. Resistance was positively associated with plant size and LMA across all populations. Other trait associations differed between native and introduced areas, implying that certain trade-offs may be fundamentally different between native and introduced populations. Our results suggest that, for the introduced populations, the loss of native herbivores and the alterations in resource availability have led to a lower diversity in leaf alkaloids among populations and may facilitate the evolution of novel trait optima without compensatory trade-offs. Such phytochemical similarity among introduced populations provides novel insights into mechanisms promoting successful plant invasions.

Methyl jasmonate-induced resistance to Delia platura (Diptera: Anthomyiidae) in Lupinus mutabilis

BACKGROUND

Andean lupin (Lupinus mutabilis Sweet) is an important leguminous crop from South America with a high protein content. In Ecuador, lupin yields are severely affected by the infestation of Delia platura larvae on germinating seeds. The application of elicitor molecules with activity against herbivorous insects to control D. platura infestation constitutes an unexplored and promising alternative for chemical insecticides. In this study, methyl jasmonate (MeJA), hexanoic acid, menadione sodium bisulfite, and DL-β-aminobutyric acid were evaluated for their ability to induce resistance against D. platura in three commercial lupin cultivars.

RESULTS

Only seeds pretreated with MeJA significantly impaired insect performance during choice and no-choice assays. Additionally, fitness indicators such as seed germination and growth were not affected by MeJA treatment. To investigate the molecular mechanisms behind the MeJA-mediated resistance, RT-qPCR assays were performed. First, RT-qPCR reference genes were validated, showing that LmUBC was the most stable reference gene. Next, expression analysis over time revealed that MeJA application up-regulated the activity of the jasmonic acid biosynthetic genes LmLOX2 and LmAOS, together with other jasmonate-related defense genes, such as LmTPS1, LmTPS4, LmPI2, LmMBL, LmL/ODC, LmCSD1, and LmPOD.

CONCLUSION

This study indicates that MeJA can be used as an environmentally friendly elicitor molecule to protect Andean lupin from D. platura attack without fitness cost. MeJA application induces plant defense responses to insects in Andean lupin that may be modulated by the onset of terpenoid biosynthesis, proteinase inhibitors, lectins, polyamines, and antioxidative enzymes. © 2021 Society of Chemical Industry.

Lupin Root Weevils (Charagmus spp., Curculionidae: Sitonini), a Lupin Pest: A Review of Their Distribution, Biology, and Challenges in Integrated Pest Management

Lupins (Lupinus spp.) are an ancient yet important legume crop. In Europe, the protein-rich seeds serve as livestock feed and have the potential to be a healthy vegetarian component of human diets. In some regions in north-eastern Europe, lupins are heavily damaged by two Curculionidae species, the lupin root weevils (LRWs) Charagmus gressorius (syn. Sitona gressorius) and Ch. griseus (syn. S. griseus). Narrow-leaved lupins (L. angustifolius) and white lupins (L. albus) are most affected. The weevils feed on lupin leaves, whereas their larvae feed on root nodules. Therefore, the larvae cause major root damage by creating lacerations that allow soil-borne plant pathogens to enter the plant tissue. These infestations lead to considerable yield losses and markedly reduced N-fixation of the root nodules. This review summarises the current knowledge on the origin, geographical distribution, and biology of these rarely described weevils. It focuses on management strategies, including preconceived insecticide use and potential ecological management methods, as key components of an integrated pest management programme against LRWs in Europe.

Metabolic Toxification of 1,2-Unsaturated Pyrrolizidine Alkaloids Causes Human Hepatic Sinusoidal Obstruction Syndrome: The Update

Saturated and unsaturated pyrrolizidine alkaloids (PAs) are present in more than 6000 plant species growing in countries all over the world. They have a typical heterocyclic structure in common, but differ in their potential toxicity, depending on the presence or absence of a double bond between C1 and C2. Fortunately, most plants contain saturated PAs without this double bond and are therefore not toxic for consumption by humans or animals. In a minority of plants, however, PAs with this double bond between C1 and C2 exhibit strong hepatotoxic, genotoxic, cytotoxic, neurotoxic, and tumorigenic potentials. If consumed in error and in large emouns, plants with 1,2-unsaturated PAs induce metabolic breaking-off of the double bonds of the unsaturated PAs, generating PA radicals that may trigger severe liver injury through a process involving microsomal P450 (CYP), with preference of its isoforms CYP 2A6, CYP 3A4, and CYP 3A5. This toxifying CYP-dependent conversion occurs primarily in the endoplasmic reticulum of the hepatocytes equivalent to the microsomal fraction. Toxified PAs injure the protein membranes of hepatocytes, and after passing their plasma membranes, more so the liver sinusoidal endothelial cells (LSECs), leading to life-threatening hepatic sinusoidal obstruction syndrome (HSOS). This injury is easily diagnosed by blood pyrrolizidine protein adducts, which are perfect diagnostic biomarkers, supporting causality evaluation using the updated RUCAM (Roussel Uclaf Causality Assessment Method). HSOS is clinically characterized by weight gain due to fluid accumulation (ascites, pleural effusion, and edema), and may lead to acute liver failure, liver transplantation, or death. In conclusion, plant-derived PAs with a double bond between C1 and C2 are potentially hepatotoxic after metabolic removal of the double bond, and may cause PA-HSOS with a potential lethal outcome, even if PA consumption is stopped.

Biologically Significant and Recently Isolated Alkaloids from Endophytic Fungi

A selection of the established and recently characterized alkaloids from the exploration of plant- and some marine-associated endophytic fungi is reviewed, with reference to alkaloids of biological significance.

Resolution of alkaloid racemate: a novel microbial approach for the production of enantiopure lupanine via industrial wastewater valorization

BACKGROUND

Lupanine is a plant toxin contained in the wastewater of lupine bean processing industries, which could be used for semi-synthesis of various novel high added-value compounds. This paper introduces an environmental friendly process for microbial production of enantiopure lupanine.

RESULTS

Previously isolated P. putida LPK411, R. rhodochrous LPK211 and Rhodococcus sp. LPK311, holding the capacity to utilize lupanine as single carbon source, were employed as biocatalysts for resolution of racemic lupanine. All strains achieved high enantiomeric excess (ee) of L-(-)-lupanine (> 95%), while with the use of LPK411 53% of the initial racemate content was not removed. LPK411 fed with lupanine enantiomers as single substrates achieved 92% of D-(+)-lupanine biodegradation, whereas L-(-)-lupanine was not metabolized. Monitoring the transcriptional kinetics of the luh gene in cultures supplemented with the racemate as well as each of the enantiomers supported the enantioselectivity of LPK411 for D-(+)-lupanine biotransformation, while (trans)-6-oxooctahydro-1H-quinolizine-3-carboxylic acid was detected as final biodegradation product from D-(+)-lupanine use. Ecotoxicological assessment demonstrated that lupanine enantiomers were less toxic to A. fischeri compared to the racemate exhibiting synergistic interaction.

CONCLUSIONS

The biological chiral separation process of lupanine presented here constitutes an eco-friendly and low-cost alternative to widely used chemical methods for chiral separation.

Chemical convergence between plants and insects: biosynthetic origins and functions of common secondary metabolites

Despite the phylogenetic distance between plants and insects, these two groups of organisms produce some secondary metabolites in common. Identical structures belonging to chemical classes such as the simple monoterpenes and sesquiterpenes, iridoid monoterpenes, cyanogenic glycosides, benzoic acid derivatives, benzoquinones and naphthoquinones are sometimes found in both plants and insects. In addition, very similar glucohydrolases involved in activating two-component defenses, such as glucosinolates and cyanogenic glycosides, occur in both plants and insects. Although this trend was first noted many years ago, researchers have long struggled to find convincing explanations for such co-occurrence. In some cases, identical compounds may be produced by plants to interfere with their function in insects. In others, plant and insect compounds may simply have parallel functions, probably in defense or attraction, and their co-occurrence is a coincidence. The biosynthetic origin of such co-occurring metabolites may be very different in insects as compared to plants. Plants and insects may have different pathways to the same metabolite, or similar sequences of intermediates, but different enzymes. Further knowledge of the ecological roles and biosynthetic pathways of secondary metabolites may shed more light on why plants and insects produce identical substances.

Lupin (Lupinus spp.) seeds exert anthelmintic activity associated with their alkaloid content

The growing range of drug resistant parasitic nematode populations threatens the sustainability of ruminant farming worldwide. In this context, nutraceuticals, animal feed that provides necessary dietary requirements while ensuring parasite control, could contribute to increase farming sustainability in developed and low resource settings. In this study, we evaluated the anthelmintic potential of lupin seed extracts against the major ruminant trichostrongylids, Haemonchus contortus and Teladorsagia circumcincta. In vitro observations showed that seed extracts from commercially available lupin varieties could significantly but moderately inhibit larval migration. This anthelmintic effect was mediated by the seed alkaloid content and was potent against both fully susceptible and multidrug resistant H. contortus isolates as well as a susceptible T. circumcincta isolate. Analytical chemistry revealed a set of four lupanine and sparteine-derivatives with anthelmintic activity, and electrophysiology assays on recombinant nematode acetylcholine receptors suggested an antagonistic mode of action for lupin alkaloids. An in vivo trial in H. contortus infected lupin-fed ewes and goats failed to demonstrate any direct anthelmintic effect of crude lupin seeds but infected lupin-fed goats suffered significantly less parasite-mediated blood losses. Altogether, our findings suggest that the anthelmintic potential of lupin remains limited. However, the potent alkaloids identified could lead to the development of novel drugs or may be used in combination with current anthelmintics to improve their efficacy.