A single amino acid determines the toxicity of Ginkgo biloba extracts

Convergent resistance to GABA receptor neurotoxins through plant-insect coevolution

The molecular mechanisms of coevolution between plants and insects remain elusive. GABA receptors are targets of many neurotoxic terpenoids, which represent the most diverse array of natural products known. Over deep evolutionary time, as plant terpene synthases diversified in plants, so did plant terpenoid defence repertoires. Here we show that herbivorous insects and their predators evolved convergent amino acid changing substitutions in duplicated copies of the Resistance to dieldrin (Rdl) gene that encodes the GABA receptor, and that the evolution of duplicated Rdl and terpenoid-resistant GABA receptors is associated with the diversification of moths and butterflies. These same substitutions also evolved in pests exposed to synthetic insecticides that target the GABA receptor. We used in vivo genome editing in Drosophila melanogaster to evaluate the fitness effects of each putative resistance mutation and found that pleiotropy both facilitates and constrains the evolution of GABA receptor resistance. The same genetic changes that confer resistance to terpenoids across 300 Myr of insect evolution have re-evolved in response to synthetic analogues over one human lifespan.

γ-Aminobutyric acid promotes the inhibition of hair growth induced by chronic restraint stress

Stress plays a critical role in hair loss, although the underlying mechanisms are largely unknown. γ-aminobutyric acid (GABA) has been reported to be associated with stress; however, whether it affects stress-induced hair growth inhibition is unclear. This study aimed to investigate the potential roles and mechanisms of action of GABA in chronic restraint stress (CRS)-induced hair growth inhibition. We performed RNA-seq analysis and found that differentially expressed genes (DEGs) associated with neuroactive ligand-receptor interaction, including genes related to GABA receptors, significantly changed after mice were treated with CRS. Targeted metabolomics analysis and enzyme-linked immunosorbent assay (ELISA) also showed that GABA levels in back skin tissues and serum significantly elevated in the CRS group. Notably, CRS-induced hair growth inhibition got aggravated by GABA and alleviated through GABA_A antagonists, such as picrotoxin and ginkgolide A. RNA sequencing analysis revealed that DEGs related to the cell cycle, DNA replication, purine metabolism, and pyrimidine metabolism pathways were significantly downregulated in dermal papilla (DP) cells after GABA treatment. Moreover, ginkgolide A, a GABA_A antagonist extracted from the leaves of Ginkgo biloba, promoted the cell cycle of DP cells. Therefore, the present study demonstrated that the increase in GABA could promote CRS-induced hair growth inhibition by downregulating the cell cycle of DP cells and suggested that ginkgolide A may be a promising therapeutic drug for hair loss.

Characterisation of thymol effects on RDL receptors from the bee parasite Varroa destructor

A major contributor to bee colony decline is infestation with its most devastating pest, the mite Varroa destructor. To control these mites, thymol is often used, although how it achieves this is not understood. One well-documented action of thymol is to modulate GABA-activated ion channels, which includes insect RDL receptors, a known insecticidal target. Here we have cloned two Varroa RDL subunits, one of which is similar to the canonical RDL subunit, while the other has some differences in M4, and, to a lesser extent, M2 and its binding site loops. Expression of this unusual RDL receptor in Xenopus oocytes reveals GABA-activated receptors, with an EC50 of 56 μM. In contrast to canonical RDL receptors, thymol does not enhance GABA-elicited responses in this receptor, and concentration response curves reveal a decrease in GABA Imax in its presence; this decrease is not seen when similar data are obtained from Apis RDL receptors. We conclude that an M2 T6'M substitution is primarily responsible for the different thymol effects, and suggest that understanding how and where thymol acts could assist in the design of novel bee-friendly miticides.

Ginkgo biloba: A Treasure of Functional Phytochemicals with Multimedicinal Applications

Ginkgo biloba is an ancient plant species that is thought to provide a variety of health benefits to living organisms and contains plenty of bioactive components, making it a chemically diversified plant. G. biloba has been shown to have a variety of medicinal and pharmacological properties, including anticancer, antidementia, antidiabetic, antiobesity, antilipidemic, antimicrobial, antioxidant, antilipid peroxidation, antiplatelet, anti-inflammatory, hepatoprotective, antidepressant, antiaging, immunomodulatory, antihypertensive, and neuroprotective effects and is frequently used to treat neurological, cardiovascular, and respiratory diseases, such as tardive dyskinesia. Therefore, this review described the therapeutic applications of G. biloba. In addition to describing the therapeutic potential, this review also evaluates the chemical constituents, toxicity, adverse effect, synergistic effect, and the clinical studies of this plant which have been utilized for therapeutic benefits but have demonstrated other consequences. The capacity of G. biloba components to act as free radical scavengers is critical, and combining its extract with other plant extracts has been shown to synergistically boost antioxidant properties. G. biloba used long-term or at high doses that resulted in some adverse effects. Severe drug interactions have also been reported in both animals and humans when combined with other medications. The available data established from both preclinical and clinical studies confirm the potential of G. biloba plant extract in various diseases. Besides, the safety and efficacy of G. biloba continue to require verification through additional experimentation to guide medicinal use.

Changes in Polar Metabolites Content during Natural and Methyl-Jasmonate-Promoted Senescence of Ginkgo biloba Leaves

The present study clarified changes in the contents of polar metabolites (amino acids, organic acids, saccharides, cyclitols, and phosphoric acid) in leaf senescence in Ginkgo biloba with or without the application of methyl jasmonate (JA-Me) in comparison with those in naturally senescent leaf blades and petioles. The contents of most amino acids and citric and malic acids were significantly higher in abaxially, and that of myo-inositol was lower in abaxially JA-Me-treated leaves than in adaxially JA-Me-treated and naturally senescent leaves. The levels of succinic and fumaric acids in leaves treated adaxially substantially high, but not in naturally senescent leaves. In contrast, sucrose, glucose, and fructose contents were much lower in leaf blades and petioles treated abaxially with JA-Me than those treated adaxially. The levels of these saccharides were also lower compared with those in naturally senescent leaves. Shikimic acid and quinic acid were present at high levels in leaf blades and petioles of G. biloba. In leaves naturally senescent, their levels were higher compared to green leaves. The shikimic acid content was also higher in the organs of naturally yellow leaves than in those treated with JA-Me. These results strongly suggest that JA-Me applied abaxially significantly enhanced processes of primary metabolism during senescence of G. biloba compared with those applied adaxially. The changes in polar metabolites in relation to natural senescence were also discussed.

Bilobalide: A review of its pharmacology, pharmacokinetics, toxicity, and safety

Bilobalide is a natural sesquiterpene trilactone from Ginkgo biloba leaves. It has good water solubility and is widely used in food and pharmaceutical fields. In the last decade, a plethora of studies on the pharmacological activities of bilobalide has been conducted and demonstrated that bilobalide possessed an extensive range of pharmacological activities such as neuroprotective, antioxidative, antiinflammatory, anti-ischemic, and cardiovascular protective activities. Pharmacokinetic studies indicated that bilobalide may have the characteristics of rapid absorption, good bioavailability, wide distribution, and slow elimination. This review aims to summarize the advances in pharmacological, pharmacokinetics, toxicity, and safety studies of bilobalide in the last decade with an emphasis on its neuroprotective and antiinflammatory activities, to provide researchers with the latest information and point out the limitations of relevant research at the current stage and the aspects that should be strengthened in future research.

Synthetic, Mechanistic, and Biological Interrogation of Ginkgo biloba Chemical Space En Route to (-)-Bilobalide

Here we interrogate the structurally dense (1.64 mcbits/Å3) GABAA receptor antagonist bilobalide, intermediates en route to its synthesis, and related mechanistic questions. 13C isotope labeling identifies an unexpected bromine migration en route to an α-selective, catalytic asymmetric Reformatsky reaction, ruling out an asymmetric allylation pathway. Experiment and computation converge on the driving forces behind two surprising observations. First, an oxetane acetal persists in concentrated mineral acid (1.5 M DCl in THF-d8/D2O); its longevity is correlated to destabilizing steric clash between substituents upon ring-opening. Second, a regioselective oxidation of des-hydroxybilobalide is found to rely on lactone acidification through lone-pair delocalization, which leads to extremely rapid intermolecular enolate equilibration. We also establish equivalent effects of (-)-bilobalide and the nonconvulsive sesquiterpene (-)-jiadifenolide on action potential-independent inhibitory currents at GABAergic synapses, using (+)-bilobalide as a negative control. The high information density of bilobalide distinguishes it from other scaffolds and may characterize natural product (NP) space more generally. Therefore, we also include a Python script to quickly (ca. 132 000 molecules/min) calculate information content (Böttcher scores), which may prove helpful to identify important features of NP space.

Concise asymmetric synthesis of (-)-bilobalide

The Ginkgo biloba metabolite bilobalide is widely ingested by humans but its effect on the mammalian central nervous system is not fully understood1-4. Antagonism of γ-aminobutyric acid A receptors (GABAARs) by bilobalide has been linked to the rescue of cognitive deficits in mouse models of Down syndrome5. A lack of convulsant activity coupled with neuroprotective effects have led some to postulate an alternative, unidentified target4; however, steric congestion and the instability of bilobalide1,2,6 have prevented pull-down of biological targets other than the GABAΑRs. A concise and flexible synthesis of bilobalide would facilitate the development of probes for the identification of potential new targets, analogues with differential selectivity between insect and human GABAΑRs, and stabilized analogues with an enhanced serum half-life7. Here we exploit the unusual reactivity of bilobalide to enable a late-stage deep oxidation that symmetrizes the molecular core and enables oxidation states to be embedded in the starting materials. The same overall strategy may be applicable to G. biloba congeners, including the ginkgolides-some of which are glycine-receptor-selective antagonists8. A chemical synthesis of bilobalide should facilitate the investigation of its biological effects and its therapeutic potential.

Phytochemicals for Improving Aspects of Cognitive Function and Psychological State Potentially Relevant to Sports Performance

Subjective alertness and optimal cognitive function, including in terms of attention, spatial/working memory and executive function, are intrinsic to peak performance in many sports. Consumption of a number of plant-derived 'secondary metabolite' phytochemicals can modulate these psychological parameters, although there is a paucity of evidence collected in a sporting context. The structural groups into which these phytochemicals fall-phenolics, terpenes and alkaloids-vary in terms of the ecological roles they play for the plant, their toxicity and the extent to which they exert direct effects on brain function. The phenolics, including polyphenols, play protective roles in the plant, and represent a natural, benign component of the human diet. Increased consumption has been shown to improve cardiovascular function and is associated with long-term brain health. However, whilst short-term supplementation with polyphenols has been shown to consistently modulate cerebral blood-flow parameters, evidence of direct effects on cognitive function and alertness/arousal is currently comparatively weak. Terpenes play both attractant and deterrent roles in the plant, and typically occur less frequently in the diet. Single doses of volatile monoterpenes derived from edible herbs such as sage (Salvia officinalis/lavandulaefolia) and peppermint (Mentha piperita), diterpene-rich Ginkgo biloba extracts and triterpene-containing extracts from plants such as ginseng (Panax ginseng/quinquefolius) and Bacopa monnieri have all been shown to enhance relevant aspects of cognitive function and alertness. The alkaloids play toxic defensive roles in the plant, including via interference with herbivore brain function. Whilst most alkaloids are inappropriate in a sporting context due to toxicity and legal status, evidence suggests that single doses of nicotine and caffeine may be able to enhance relevant aspects of cognitive function and/or alertness. However, their benefits may be confounded by habituation and withdrawal effects in the longer term. The efficacy of volatile terpenes, triterpene-rich extracts and products combining low doses of caffeine with other phytochemicals deserves more research attention.

Ginkgolic acids induce HepG2 cell death via a combination of apoptosis, autophagy and the mitochondrial pathway

Ginkgolic acids may induce malignant cell death via the B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax)/Bcl-2 apoptosis pathway. Concurrently, apoptosis, autophagy and mitochondrial dysfunction may also be involved in bringing about this endpoint. The anticancer effect of Ginkgolic acids (GAs) was investigated using the HepG2 cell line. The median lethal dose of the GAs of the HepG2 was measured via an MTT assay, the dose-response curves were evaluated and changes in cell morphology were monitored by microscopy. Autophagy in HepG2 cells was down regulated using 3-methyladenine (3-MA) or Beclin-1-specific small interfering RNA (siRNA) and the expression of apoptosis associated proteins caspase-3, Bax/Bcl-2, and the autophagy-associated protein 5 and microtubule-associated protein 1A/1B-light chain 3 in the GA-treated HepG2 cells were all measured by western blot analysis. The level of apoptosis in the GA-treated cells was also assessed using terminal deoxynucleotidyl-transferase-mediated dUTP nick-end labeling (TUNEL) assay, and the mitochondrial membrane potential (Δψ_m) was detected by immunofluorescence. The results of the MTT and TUNEL assays indicated that the proliferation of HepG2 cells treated with GAs was significantly reduced compared with the control group, and the rate of the inhibition was dose-dependent. Western blot analysis indicated that treatment with the Gas induced apoptosis and autophagy in the HepG2 cells. The Δψ_m of the GA-treated HepG2 cells was decreased compared with the control, as monitored by immunofluorescence. However, upon the administration of 3-MA or Beclin-1-specific siRNAs (inhibitors of the autophagy), the expression levels of the apoptosis- and autophagy-associated proteins were decreased. In conclusion, the results of the present study indicated that GAs are potent anticancer agents that function through a combination of the apoptosis, autophagy and mitochondrial pathways.

Review of Ginkgo biloba-induced toxicity, from experimental studies to human case reports

Ginkgo biloba seeds and leaves have been used as a traditional herbal remedy for thousands of years, and its leaf extract has been consumed as a botanical dietary supplement for decades. Ginkgo biloba extract is a complex mixture with numerous components, including flavonol glycosides and terpene lactones, and is one of the most widely sold botanical dietary supplements worldwide. Concerns about potential health risks for the general population have been raised because of the widespread human exposure to Ginkgo biloba and its potential toxic and carcinogenic activities in rodents. The National Toxicology Program conducted 2-year gavage studies on one Ginkgo biloba leaf extract and concluded that there was clear evidence of carcinogenic activity of this extract in mice based on an increased incidence of hepatocellular carcinoma and hepatoblastoma. Recently, Ginkgo biloba leaf extract has been classified as a possible human carcinogen (Group 2B) by the International Agency for Research on Cancer. This review presents updated information on the toxicological effects from experimental studies both in vitro and in vivo to human case reports (caused by ginkgo seeds or leaves), and also summarizes the negative results from relatively large clinical trials.

An atypical residue in the pore of Varroa destructor GABA-activated RDL receptors affects picrotoxin block and thymol modulation

GABA-activated RDL receptors are the insect equivalent of mammalian GABAA receptors, and play a vital role in neurotransmission and insecticide action. Here we clone the pore lining M2 region of the Varroa mite RDL receptor and show that it has 4 atypical residues when compared to M2 regions of most other insects, including bees, which are the major host of Varroa mites. We create mutant Drosophila RDL receptors containing these substitutions and characterise their effects on function. Using two electrode voltage clamp electrophysiology we show that one substitution (T6'M) ablates picrotoxin inhibition and increases the potency of GABA. This mutation also alters the effect of thymol, which enhances both insect and mammalian GABA responses, and is widely used as a miticide. Thymol decreases the GABA EC50 of WT receptors, enhancing responses, but in T6'M-containing receptors it is inhibitory. The other 3 atypical residues have no major effects on either the GABA EC50, the picrotoxin potency or the effect of thymol. In conclusion we show that the RDL 6' residue is important for channel block, activation and modulation, and understanding its function also has the potential to prove useful in the design of Varroa-specific insecticidal agents.

Discriminating between 5-HT₃A and 5-HT₃AB receptors

The 5-HT3B subunit was first cloned in 1999, and co-expression with the 5-HT3A subunit results in heteromeric 5-HT₃AB receptors that are functionally distinct from homomeric 5-HT₃A receptors. The affinities of competitive ligands at the two receptor subtypes are usually similar, but those of non-competitive antagonists that bind in the pore often differ. A competitive ligand and allosteric modulator that distinguishes 5-HT₃A from 5-HT₃AB receptors has recently been described, and the number of non-competitive antagonists identified with this ability has increased in recent years. In this review, we discuss the differences between 5-HT₃A and 5-HT₃AB receptors and describe the possible sites of action of compounds that can distinguish between them.

A single channel mutation alters agonist efficacy at 5-HT3A and 5-HT3AB receptors

BACKGROUND AND PURPOSE

5-HT₃ receptors are composed of 5-HT₃A subunits (homomeric receptors), or combinations of 5-HT₃A and other 5-HT₃ receptor subunits (heteromeric receptors, the best studied of which are 5-HT₃AB receptors). Here we explore the effects of partial agonists at 5-HT₃A and 5-HT₃AB receptors, and the importance of a channel-lining residue in determining the efficacy of activation.

EXPERIMENTAL APPROACH

Wild type and mutant 5-HT₃A and 5-HT₃AB receptors were expressed in Xenopus oocytes and examined using two-electrode voltage-clamp, or expressed in HEK293 cells and examined using [³H]granisetron binding.

KEY RESULTS

Dopamine, quipazine and VUF10166 were partial agonists at wild type 5-HT₃A and 5-HT₃AB receptors, with quipazine and VUF10166 causing a long-lived (>20 min) inhibition of subsequent agonist responses. At 5-HT₃A receptors, mCPBG was a partial agonist, but was a superagonist at 5-HT₃AB receptors, as it produced a response 2.6× greater than that of 5-HT. A T6'S substitution in the 5-HT₃A subunit decreased EC₅₀ and increased R_max of dopamine and quipazine at both homomeric and heteromeric receptors. The greatest changes were seen with VUF10166 at 5-HT₃A_T6'SB receptors, where it became a full agonist (EC₅₀ = 7 nM) with an EC₅₀ 58-fold less than 5-HT (EC₅₀ = 0.4 μM) and no longer caused inhibition of subsequent agonist responses.

CONCLUSIONS AND IMPLICATIONS

These results indicate that a mutation in the pore lining domain in both 5-HT₃A and 5-HT₃AB receptors alters the relative efficacy of a series of agonists, changing some (e.g. quipazine) from apparent antagonists to potent and efficacious agonists.

Mixed antagonistic effects of the ginkgolides at recombinant human ρ1 GABAC receptors

The diterpene lactones of Ginkgo biloba, ginkgolides A, B and C are antagonists at a range of Cys-loop receptors. This study examined the effects of the ginkgolides at recombinant human ρ(1) GABA(C) receptors expressed in Xenopus oocytes using two-electrode voltage clamp. The ginkgolides were moderately potent antagonists with IC(50)s in the μM range. At 10 μM, 30 μM and 100 μM, the ginkgolides caused rightward shifts of GABA dose-response curves and reduced maximal GABA responses, characteristic of noncompetitive antagonists, while the potencies showed a clear dependence on GABA concentration, indicating apparent competitive antagonism. This suggests that the ginkgolides exert a mixed-type antagonism at the ρ(1) GABA(C) receptors. The ginkgolides did not exhibit any obvious use-dependent inhibition. Fitting of the data to a number of kinetic schemes suggests an allosteric inhibition as a possible mechanism of action of the ginkgolides which accounts for their inhibition of the responses without channel block or use-dependent inhibition. Kinetic modelling predicts that the ginkgolides exhibit saturation of antagonism at high concentrations of GABA, but this was only partially observed for ginkgolide B. It also suggests that there may be different binding sites in the closed and open states of the receptor, with a higher affinity for the receptor in the closed state.