Glycosides of the Neurotoxin Tutin in Toxic Honeys Are from Coriaria arborea Phloem Sap, Not Insect Metabolism

Picrotoxane sesquiterpenoids: chemistry, chemo- and bio-syntheses and biological activities

Covering: up to December 2021Picrotoxane sesquiterpenoids are a special category of natural products known to have a picrotoxane skeleton and are characterised by a highly oxidised cis-hydrindene core, lactone rings, and epoxide functionalities. Ever since the first picrotoxane was isolated from Menispermum cocculus in the early 19^th century, these compounds have long attracted the attention of natural product chemists, synthetic chemists, and pharmacologists for their particular structures and powerful biological activities. This review extensively summarizes a total of 132 naturally occurring picrotoxane sesquiterpenoids, taking into account their distributions, structural classifications, chemical and bio-synthetic researches, and bioactivities. It provides a comprehensive and in-depth perspective for further investigation on picrotoxane sesquiterpenoids.

Natural plant toxins in honey: An ignored threat to human health

Consumers often believe that "natural food" is harmless, however naturally occurring toxins in food represent a health risk to humans. Honey as a natural, nutritious sweetener, is one of the most commonly consumed foods throughout the world. However, food safety concerns for honey arise when honeybees collect nectar from poisonous plants such as Rhododendron sp., Coriaria arborea, and Tripterygium wilfordii Hook F. Such honey contains natural plant toxins. Humans may develop intoxication symptoms after consuming toxic honey; in some cases, it can be fatal. As a result, toxic honey poses an often-ignored threat to public health. Typical plant toxins such as grayanotoxins, triptolides, tutin and pyrrolizidine alkaloids, have been identified in toxic honey. Although different toxic honeys elicit similar symptoms, such as vomiting, nausea, and dizziness, the mechanism of toxicity may be different. Thus, it is necessary to determine the exact toxicity mechanism of different toxins to further develop effective antidotes and cures. Another important challenge is preventing toxic honey from entering the food chain. Liquid chromatography-mass spectrometry has a wide range of applications in the detection of different toxins due to its accuracy and simplicity. More methods, however, are urgently needed to detect multiple plant-derived toxins in honey and its derivatives. Developing uniform international standards for toxin detection during quarantine using advanced techniques is critical for preventing human consumption of toxic honey.

An ethnobotanical study of forage plants in Zhuxi County in the Qinba mountainous area of central China

In the Qinba mountainous area of Central China, pig farming has a significant impact on the growth of the rural economy and has substantially increased farmer incomes. Traditional knowledge plays an important role in the selection of forage plant species for pig farming by local people. This study aimed to identify the forage plants used for pig feeding and to catalog indigenous knowledge regarding their use. During 2016 and 2017, ethnobotanical surveys and inventories were conducted in Zhuxi County, Hubei Province, China. Data were collected using semi-structured interviews, key informant reports, free listings, guided field walks, and participatory observations with 77 households in 16 villages in 13 towns/townships. The obtained data were analyzed using a relative frequency citation (RFC) index. Overall, 145 wild forage plants from 91 genera and 31 families were recorded. The most cited families were Asteraceae, Polygonaceae, Urticaceae, Amaranthaceae, Fabaceae, Cruciferae, Caryophyllaceae, and Lamiaceae. Whole plants (75.9%) and tender leaves (12.4%) were the most frequently used parts of the plants. Most of the forage plants were herbaceous (88.9%). Almost all forage plants could be collected throughout the year (62.7%). Raw and cooked were the two main preparation methods. The most frequently cited species were Taraxacum mongolicum, Bidens pilosa, Sonchus oleraceus, Pilea verrucosa, and Pilea pumila var. obtusifolia. A total of 14 species were identified as the top forage plants in Zhuxi County based on their RFC values (RFC value greater than 0.5). Local people possess rich traditional knowledge about the utilization and management of forage plants for pig feeding. However, the maintenance of this traditional knowledge may be seriously threatened by changes in pig feeding modes and the lack of successors. Appropriate strategies and action plans have been suggested for the conservation of traditional knowledge associated with biodiversity and the sustainable use of forage species resources. These include 1) taking targeted measures to protect forage resources and associated traditional knowledge; 2) strengthening research on the forage plants with the highest RFC values for nutritional value, digestibility, other functions, and ecological status; and 3) enhancing the identification of poisonous forage plants.

Gelsedine-type alkaloids: Discovery of natural neurotoxins presented in toxic honey

The fascinating collection and evaluation of natural products with enormous structural and chemical diversity can contribute to ensure human health and inspire potential drug discovery. We reported the identification of 14-(R)-hydroxy-gelsenicine (HGE), a new component from poisonous honey, which has recently caused multiple serious intoxications and deaths up on consumption. The prevalence, toxicity, toxicokinetics and metabolic profile of HGE were evaluated through in vitro and in vivo analyses. HGE is a very toxic substance and shows significant gender difference with LD₅₀ of 0.125 mg kg^-1 and 0.295 mg kg^-1 for the female and male mice, respectively. Toxicokinetics test indicates that HGE has good bioavailability in rats, and is metabolized extensively, in which hydroxylation, reduction, N-demethyl ether and glucuronication are the major metabolic pathways. Additionally, HGE shows specific neurotoxicity by enhancing the binding of γ-aminobutyric acid (GABA) to its receptors. We found that flumazenil, a selective antagonist of GABA receptor, could effectively increase the survival of the tested animals, which provides a potential therapy for future clinical applications.

Actinorhizal trees and shrubs from Africa: distribution, conservation and uses

Actinorhizal plants are a group of perennial dicotyledonous angiosperms, comprised of more than 200 species, most of which can establish root-nodule symbiosis with the nitrogen fixing actinobacteria of the genus Frankia. They are key providers of fundamental goods and services and can give a major contribution to mitigate the combined effects of climate changes, human population growth and loss of biodiversity. This aspect is particularly relevant for the developing economies of many African countries, which are highly exposed to climate and anthropogenic disturbances. In this work we have analyzed the distribution, conservation and uses of actinorhizal species native to or introduced in Africa. A total of 42 taxa distributed over six botanical families (Betulaceae, Casuarinaceae, Myricaceae, Elaeagnaceae, Rhamnaceae and Coriariaceae) were identified. The vast majority is able to thrive under a range of diverse environments and has multiple ecological and economic potential. More than half of the identified species belong to the genus Morella (Myricaceae), most of them native to Middle, Eastern and Southern Africa. Although the information about the conservation status and uses of Morella spp. is largely incomplete, the available data is indicative of their potential in e.g. forestry and agroforestry, food and medicine. Therefore, efforts should be made to upgrade actinorhizal research in Africa towards the sustainable use of biodiversity at the service of local (bio)economies.