Biosynthesis of 4'-O-methylpyridoxine (Ginkgotoxin) from primary precursors

A critical review of current technologies used to reduce ginkgotoxin, ginkgotoxin-5'-glucoside, ginkgolic acid, allergic glycoprotein, and cyanide in Ginkgo biloba L. seed

The Ginkgo biloba has astonished scholars globally with enormous bioactives, with sales exceeding $10 billion since 2017. The Ginkgo biloba seed (GBS) is an essential part of culinary culture. Nevertheless, toxins in fresh Ginkgo biloba seed (GBS) have limited GBSs' daily consumption. Ginkgotoxin and ginkgotoxin-5-glucoside cause poisoning, tonic-clonic convulsions, and neurotoxic effects. Ginkgolic acid causes cytotoxicity and allergies. Allergic glycoprotein in GBS causes nausea, seizures, dyspnea, mydriasis, vomiting, and bellyache. The amygdalin-derived hydrocyanic acid cause dizziness, vomiting, cramping, and sleeping disorders. Food products are frequently exposed to various processing techniques to increase food safety and functionality. As a result, this review focused on the technologies that have been used to minimize toxins in GBS. In addition, a comparison of these techniques was made based on their benefits, drawbacks, feasibility, pharmacological activities, and future direction or opportunities to improve current ones were provided.

Preparation of ZIF-8 and Its Application in Determination of Pyridoxine and Pyridoxal in Ginkgo Seeds by Ultra-Performance Liquid Chromatography

A new rapid and accurate method was developed for simultaneous determination of pyridoxine and pyridoxal in ginkgo seeds, using ultra-performance liquid chromatography (UPLC) equipped with a fluorescence detector. Diluted hydrochloric acid solution was used as the extracting solvent. For the pretreatment of extracts, a zeolitic imidazolate framework material (ZIF-8) was prepared and characterized. An ODS-BP column (4.6 mm × 250 mm × 5 μm) was used for separation. The conditions of sample extraction, cleaning and separation were optimized. The linear correlation coefficient (R²) of the analyte was better than 0.9999, indicating good linearity. The limits of detection (LODs) of pyridoxal and pyridoxine were 0.0065 mg/kg and 0.0057 mg/kg, respectively, and limits of quantitation (LOQs) were 0.022 mg/kg and 0.019 mg/kg, respectively. The recovery of the two substances ranged from 86.2% to 110.4%, and the relative standard deviation (n = 6) was less than 7.5%. The method was applied to determine the contents of pyridoxine and pyridoxal in actual ginkgo seed samples with satisfactory results.

Traversing through half a century research timeline on Ginkgo biloba, in transforming a botanical rarity into an active functional food ingredient

Neurodegenerative diseases and various other chronic ailments have gradually transformed into public-health issues. Neurodegenerative disorders are a range of progressive neural abnormalities characterized by cellular dysfunctions, neuronal structure, and function loss. Among many chronic disorders, oxidative stress, inflammation, mitochondrial dysregulation, and cellular alterations in the human body are considered the most prevalent diagnostic symptoms. They have a profound impact on patients' health and wellbeing. The disease's poor curability, high healthcare costs, and lethality are the principal reasons for approaching and exploring the conventional treatment's phytotherapeutic alternatives. Ginkgo biloba (Maidenhair tree) is a well-known and widely used herbal plant in the Ginkgoaceae family. Its phytochemical constituents, Flavonoids, and terpenes, have been identified as the primary ingredients of Ginkgo biloba leaf extracts. It has been widely used due to its therapeutic properties, including its neuroprotective, anti-dementia, antioxidant, anti-inflammatory, vasoactive, anti-psychotic, anti-neoplastic, and anti-platelet activity. In recent decades, plenty of Ginkgo-derived substances has been researched and elucidated to have significant therapeutic effects in numerous disease models. This review aims to provide a thorough understanding of the botanical basis for Ginkgo biloba, its usage as herbal medicine, and its pivotal role in functional foods. Additionally, the clinical significance of Ginkgo biloba, as observed in various research works and clinical investigations, is also emphasized, facilitating a better understanding of their molecular basis and application in many chronic diseases.

A Facile Method to Determine the Native Contents of 4'-O-Methylpyridoxine and 4'-O-Methylpyridoxine-5'-glucoside in Ginkgo biloba Seeds

4'-O-Methylpyridoxine (MPN) and MPN-5'-glucoside (MPNG) are collectively known as ginkgotoxin, which are the main toxic ingredients of excessive consumption of Ginkgo biloba seeds. Water extraction is the generally adopted sample preparation method for high-performance liquid chromatography determination of ginkgotoxin. However, endogenous enzymes such as glycosidases in Ginkgo biloba seeds can hydrolyze MPNG to MPN in the process of water extraction, which will result in the measured contents of MPN and MPNG but not their natural contents in Ginkgo biloba seeds. In this work, inhibitors for the endogenous enzymes were first screened, and it was found that silver fluoride could effectively inhibit endogenous enzymes such as glucosidase and phosphatase. The optimized concentration of silver fluoride was 25 mmol/L, which could effectively inhibit the endogenous enzymes for more than 60 h. A new sample preparation method based on water extraction with 25 mmol/L silver fluoride addition was thus developed. This method was employed to determine the native contents of MPN and MPNG in the exotesta and kernel of five Ginkgo biloba seed cultivars. The result showed that the contents of MPNG in the exotesta and kernel of five cultivars were significantly higher than those of MPN. MPNG was present at high content in raw seeds, which was the main form of ginkgotoxin in seeds. The method established in this work is simple and effective and can be used to accurately quantify the native contents of MPN and MPNG.

In vivo toxicity assessment of 4'-O-methylpyridoxine from Ginkgo biloba seeds: Growth, hematology, metabolism, and oxidative parameters

4'-O-methylpyridoxine (MPN), a recognized antivitamin B₆ compound, is a potentially poisonous substance found in Ginkgo biloba seeds and leaves. In this work, the body weights, histopathological changes, plasma vitamin B₆ (VB₆), biochemical parameters, oxidative stress responses, and amino acids of rats were investigated after intragastric administration of MPN for 15 days. Results showed that intragastric administration of 50 mg/kg BW MPN caused pathological changes in the brain and heart tissues of rats. Administration of 10 mg/kg and 30 mg/kg BW MPN can significantly increase VB₆ analogs in the plasma of rats, such as pyridoxal-5'-phosphate, pyridoxal. Results of biochemical parameters indicated that MPN can damage brains and hearts by changing the enzyme activity of these organs. These results suggest that consumption of Ginkgo biloba seeds for the long term, even in a small quantity, may lead to poisoning.

4'-O-methylpyridoxine: Preparation from Ginkgo biloba Seeds and Cytotoxicity in GES-1 Cells

Ginkgo biloba seeds are wildly used in the food and medicine industry. It has been found that 4′-O-methylpyridoxine (MPN) is responsible for the poisoning caused by G. biloba seeds. The objective of this study was to explore and optimize the extraction method of MPN from G. biloba seeds, and investigate its toxic effect on human gastric epithelial cells (GES-1) and the potential related mechanisms. The results showed that the extraction amount of MPN was 1.933 μg/mg, when extracted at 40 °C for 100 min, with the solid–liquid ratio at 1:10. MPN inhibited the proliferation of GES-1 cells, for which the inhibition rate was 38.27% when the concentration of MPN was 100 μM, and the IC₅₀ value was 127.80 μM; meanwhile, the cell cycle was arrested in G2 phase. High concentration of MPN (100 μM) had significant effects on the nucleus of GES-1 cells, and the proportion of apoptotic cells reached 43.80%. Furthermore, the Western blotting analysis showed that MPN could reduce mitochondrial membrane potential by increasing the expression levels of apoptotic proteins Caspase 8 and Bax in GES-1 cells. In conclusion, MPN may induce apoptosis in GES-1 cells, which leads to toxicity in the human body.

Effects of roasting conditions on physicochemical properties and antioxidant activities in Ginkgo biloba seeds

The roasting treatment has been used to extend the shelf life of food and improves its quality, and eliminate or reduce toxic. In this study, we investigate the changes in the physicochemical properties and antioxidant activities of Ginkgo biloba seeds (GBS) according to the roasting temperature and duration. As the roasting temperature and duration increased, the pH (from 7.32 to 6.31) and total cyanide content (from 1.49 to 0.70 µg/g) decreased, whereas the titratable acidity (from 0.39 to 0.84%) increased. The antioxidant activities increased rapidly at 210 °C according to the increase in the roasting temperature and duration. The 4'-O-methylpyridoxine (MPN) content in the 210 °C heat treatment group decreased by more than 70% compared to the MPN content in the control group. These results suggest that heat-treated GBS could be used in food materials and medicines for decreasing cyanide and MPN contents as well as for increasing antioxidant compound contents.

Determination and Comparison of 4'- O-Methylpyridoxine Analogues in Ginkgo biloba Seeds at Different Growth Stages

The antivitamin B₆, 4'- O-methylpyridoxine (MPN); its glucoside, 4'- O-methylpyridoxine-5'-glucoside (MPNG); and vitamin B₆ compounds, including pyridoxal (PL), pyridoxamine, pyridoxine, pyridoxal-5'-phosphate (PLP), and pyridoxamine-5'-phosphate, exist in Ginkgo biloba seeds, which are widely used as food and medicine. This work aimed to determine the MPN analogues in G. biloba seeds at different growth stages in terms of cultivars and ages of trees. The highest total MPN contents of 249.30, 295.62, and 267.85 μg/g were obtained in the mature stages of three selected G. biloba samples. The total contents of vitamin B₆ compounds decreased significantly in the entire growth period of the three samples. Principal-component analysis revealed that MPN and MPNG were important contributors in the MPN-analogue metabolism of G. biloba seeds. The influence of the cultivar on the content and composition of MPN analogues was greater than that of the age of the G. biloba tree.

Natural riboflavin analogs

Riboflavin analogs have a good potential to serve as basic structures for the development of novel anti-infectives. Riboflavin analogs have multiple cellular targets, since riboflavin (as a precursor to flavin cofactors) is active at more than one site in the cell. As a result, the frequency of developing resistance to antimicrobials based on riboflavin analogs is expected to be significantly lower. The only known natural riboflavin analog with antibiotic function is roseoflavin from the bacterium Streptomyces davawensis. This antibiotic negatively affects flavoenzymes and FMN riboswitches. Another roseoflavin producer, Streptomyces cinnabarinus, was recently identified. Possibly, flavin analogs with antibiotic activity are more widespread than anticipated. The same could be true for flavin analogs yet to be discovered, which could constitute tools for cellular chemistry, thus allowing a further extension of the catalytic spectrum of flavoenzymes.

Genome sequence of the bacterium Streptomyces davawensis JCM 4913 and heterologous production of the unique antibiotic roseoflavin

Streptomyces davawensis JCM 4913 synthesizes the antibiotic roseoflavin, a structural riboflavin (vitamin B(2)) analog. Here, we report the 9,466,619-bp linear chromosome of S. davawensis JCM 4913 and a 89,331-bp linear plasmid. The sequence has an average G+C content of 70.58% and contains six rRNA operons (16S-23S-5S) and 69 tRNA genes. The 8,616 predicted protein-coding sequences include 32 clusters coding for secondary metabolites, several of which are unique to S. davawensis. The chromosome contains long terminal inverted repeats of 33,255 bp each and atypical telomeres. Sequence analysis with regard to riboflavin biosynthesis revealed three different patterns of gene organization in Streptomyces species. Heterologous expression of a set of genes present on a subgenomic fragment of S. davawensis resulted in the production of roseoflavin by the host Streptomyces coelicolor M1152. Phylogenetic analysis revealed that S. davawensis is a close relative of Streptomyces cinnabarinus, and much to our surprise, we found that the latter bacterium is a roseoflavin producer as well.

Crystal structures of human pyridoxal kinase in complex with the neurotoxins, ginkgotoxin and theophylline: insights into pyridoxal kinase inhibition

Several drugs and natural compounds are known to be highly neurotoxic, triggering epileptic convulsions or seizures, and causing headaches, agitations, as well as other neuronal symptoms. The neurotoxic effects of some of these compounds, including theophylline and ginkgotoxin, have been traced to their inhibitory activity against human pyridoxal kinase (hPL kinase), resulting in deficiency of the active cofactor form of vitamin B₆, pyridoxal 5'-phosphate (PLP). Pyridoxal (PL), an inactive form of vitamin B₆ is converted to PLP by PL kinase. PLP is the B₆ vitamer required as a cofactor for over 160 enzymatic activities essential in primary and secondary metabolism. We have performed structural and kinetic studies on hPL kinase with several potential inhibitors, including ginkgotoxin and theophylline. The structural studies show ginkgotoxin and theophylline bound at the substrate site, and are involved in similar protein interactions as the natural substrate, PL. Interestingly, the phosphorylated product of ginkgotoxin is also observed bound at the active site. This work provides insights into the molecular basis of hPL kinase inhibition and may provide a working hypothesis to quickly screen or identify neurotoxic drugs as potential hPL kinase inhibitors. Such adverse effects may be prevented by administration of an appropriate form of vitamin B₆, or provide clues of how to modify these drugs to help reduce their hPL kinase inhibitory effects.

Ginkgo biloba and ginkgotoxin

Products prepared from Ginkgo biloba are top-selling phytopharmaceuticals especially in Europe and major botanical dietary supplements in the United States. In European medicine, G. biloba medications are used to improve memory, to treat neuronal disorders such as tinnitus or intermittent claudication, and to improve brain metabolism and peripheral blood flow. The whole array of indications is reflected by a number of defined natural product constituents in G. biloba. The most well-known ones are flavonoids and terpene lactones, but they also include allergenic and toxic compounds such as ginkgotoxin (1). Consequently, there are reports attributing beneficial as well as adverse effects to G. biloba products. The present paper summarizes recent experiences with G. biloba and its derived products and explains why their restricted use is recommended.

Vitamin B6: a long known compound of surprising complexity

In recent years vitamin B6 has become a focus of research describing the compound’s critical function in cellular metabolism and stress response. For many years the sole function of vitamin B6 was considered to be that of an enzymatic cofactor. However, recently it became clear that it is also a potent antioxidant that effectively quenches reactive oxygen species and is thus of high importance for cellular well-being. In view of the recent findings, the current review takes a look back and summarizes the discovery of vitamin B6 and the elucidation of its structure and biosynthetic pathways. It provides a detailed overview on vitamin B6 both as a cofactor and a protective compound. Besides these general characteristics of the vitamin, the review also outlines the current literature on vitamin B6 derivatives and elaborates on recent findings that provide new insights into transport and catabolism of the compound and on its impact on human health.

The Pdx1 family is structurally and functionally conserved between Arabidopsis thaliana and Ginkgo biloba

Vitamin B6 is one of the most important compounds in living organisms, and its biosynthesis has only recently been understood. Because it is required for more than 100 biochemical reactions, lack of the vitamin is fatal. This is of special importance to mammals and humans, which cannot biosynthesize the vitamin and thus depend on its external uptake. Here we describe the cloning of a vitamin B6 biosynthetic gene GbPDX1 from Ginkgo biloba. The gene is expressed in seeds, leaf and trunk tissue. Using yeast 2-hybrid and pull-down assays, we show that the protein can interact with itself and with members of Arabidopsis thaliana AtPDX1 and AtPDX2 families. Furthermore, we prove the function of GbPDX1 in vitamin B6 biosynthesis by complementation of an Arabidopsis AtPDX1.3 mutant rsr4-1, at the phenotypical level and increasing vitamin B6 levels caused by ectopic GbPDX1 expression in the mutant background. Overall, this study provides a first description of Ginkgo vitamin B6 metabolism, and demonstrates a high degree of conservation between Ginkgo and Arabidopsis.

Herbal medicine and epilepsy: proconvulsive effects and interactions with antiepileptic drugs

The use of complementary and alternative medicine is on the rise, including among patients with epilepsy. Herbal medicine, one of the most popular forms of CAM, is considered to be both safe and effective by most consumers. Yet many herbs may increase the risk for seizures, through intrinsic proconvulsant properties or contamination by heavy metals, as well as via effects on the cytochrome P450 enzymes and P-glycoproteins, altering antiepileptic drug (AED) disposition. Herb-drug interactions may be difficult to predict, especially since the quality and quantity of active ingredients are often unknown. Since most patients do not inform their physicians that they are taking herbal medicines, health care professionals must initiate a dialogue in order to prevent complications with the combined regimen. At the same time, further research is required regarding the effect of herbs on seizure activity and interactions with AED treatment.

PDX1 is essential for vitamin B6 biosynthesis, development and stress tolerance in Arabidopsis

Vitamin B6 is an essential coenzyme for numerous metabolic enzymes and is a potent antioxidant. In plants, very little is known about its contribution to viability, growth and development. The de novo pathway of vitamin B6 biosynthesis has only been described recently and involves the protein PDX1 (pyridoxal phosphate synthase protein). Arabidopsis thaliana has three homologs of PDX1, two of which, PDX1.1 and PDX1.3, have been demonstrated as functional in vitamin B6 biosynthesis in vitro and by yeast complementation. In this study, we show that the spatial and temporal expression patterns of PDX1.1 and PDX1.3, investigated at the transcript and protein level, largely overlap, but PDX1.3 is more abundant than PDX1.1. Development of single pdx1.1 and pdx1.3 mutants is partially affected, whereas disruption of both genes causes embryo lethality at the globular stage. Detailed examination of the single mutants, in addition to those that only have a single functional copy of either gene, indicates that although these genes are partially redundant in vitamin B6 synthesis, PDX1.3 is more requisite than PDX1.1. Developmental distinctions correlate with the vitamin B6 content. Furthermore, we provide evidence that in addition to being essential for plant growth and development, vitamin B6 also plays a role in stress tolerance and photoprotection of plants.

Vitamin B6 biosynthesis in higher plants

Vitamin B6 is an essential metabolite in all organisms. It can act as a coenzyme for numerous metabolic enzymes and has recently been shown to be a potent antioxidant. Plants and microorganisms have a de novo biosynthetic pathway for vitamin B6, but animals must obtain it from dietary sources. In Escherichia coli, it is known that the vitamin is derived from deoxyxylulose 5-phosphate (an intermediate in the nonmevalonate pathway of isoprenoid biosynthesis) and 4-phosphohydroxy-l-threonine. It has been assumed that vitamin B6 is synthesized in the same way in plants, but this hypothesis has never been experimentally proven. Here, we show that, in plants, synthesis of the vitamin takes an entirely different route, which does not involve deoxyxylulose 5-phosphate but instead utilizes intermediates from the pentose phosphate pathway, i.e., ribose 5-phosphate or ribulose 5-phosphate, and from glycolysis, i.e., dihydroxyacetone phosphate or glyceraldehyde 3-phosphate. The revelation is based on the recent discovery that, in bacteria and fungi, a novel pathway is in place that involves two genes (PDX1 and PDX2), neither of which is homologous to any of those involved in the previously doctrined E. coli pathway. We demonstrate that Arabidopsis thaliana has two functional homologs of PDX1 and a single homolog of PDX2. Furthermore, and contrary to what was inferred previously, we show that the pathway appears to be cytosolic and is not localized to the plastid. Last, we report that the single PDX2 homolog is essential for plant viability.

Biosynthesis of vitamin B(6) in yeast: incorporation pattern of glucose

Two yeasts, Saccharomyces cerevisiae ATCC 7752 and Candida utilis ATCC 9256, were incubated in the presence of variously multiply (13)C-labeled samples of D-glucose. The (13)C incorporation pattern within pyridoxamine dihydrochloride, established by (13)C NMR spectroscopy, differed from that which had previously been found within pyridoxine, isolated from Escherichia coli. Thus, the origin of the carbon skeleton of vitamin B(6) in yeast differs substantially from its origin in E. coli. In particular, in yeast the distribution of (13)C within the C(5) chain C-2',2,3,4,4' of pyridoxamine corresponds to the distribution of (13)C within the C(5) chain C-1,2,3,4,5 of the ribose component of cytidine. It follows that the C(5) chains of pyridoxamine and of ribose originate from a common glucose-derived pentulose or pentose intermediate. By contrast, in E. coli the C(5) chain of pyridoxine is derived from 1-deoxy-D-xylulose 5-phosphate which, in turn, originates by condensation of pyruvic acid with glyceraldehyde 3-phosphate.

Biosynthesis of vitamin B6 and structurally related derivatives

In spite of the rather simple structure of pyridoxal 5'-phosphate (I), a member of the vitamin B6 group, the elucidation of its de novo biosynthesis remained largely unexplored until recently. Experiments designed to investigate the formation of the vitamin B6 pyridine nucleus mainly concentrated on Escherichia coli. The results of tracer experiments with radioactive and stable isotopes, feeding experiments, and molecular biological studies led to the prediction that 4-hydroxy-L-threonine (VIII, R = H) and 1-deoxy-D-xylulose (VII, R = H) are precursors which are assembled to yield the carbon-nitrogen skeleton of vitamin B6. At this point, the involvement of the phosphorylated forms of these precursors in this assembly seems quite clear. However, vitamin B6 biosynthesis in organisms other than E. coli remains largely unknown. Toxic derivatives of vitamin B6, such as ginkgotoxin, occurring in higher plants may be suitable targets to gain further insight into this tricky problem.

Pharmacognosy in the 21st century

The term pharmacognosy as a constituent scientific discipline of pharmacy has been in use for nearly 200 years, and it refers to studies on natural product drugs. During the last half of the 20th century, pharmacognosy evolved from being a descriptive botanical subject to one having a more chemical and biological focus. At the beginning of the 21st century, pharmacognosy teaching in academic pharmacy institutions has been given new relevance, as a result of the explosive growth in the use of herbal remedies (phytomedicines) in modern pharmacy practice, particularly in western Europe and North America. In turn, pharmacognosy research areas are continuing to expand, and now include aspects of cell and molecular biology in relation to natural products, ethnobotany and phytotherapy, in addition to the more traditional analytical method development and phytochemistry. Examples are provided in this review of promising bioactive compounds obtained in two multidisciplinary natural product drug discovery projects, aimed at the elucidation of new plant-derived cancer chemotherapeutic agents and novel cancer chemopreventives, respectively. The systematic study of herbal remedies offers pharmacognosy groups an attractive new area of research, ranging from investigating the biologically active principles of phytomedicines and their mode of action and potential drug interactions, to quality control, and involvement in clinical trials.