Lowered sensitivity of bitter taste receptors to β-glucosides in bamboo lemurs: an instance of parallel and adaptive functional decline in TAS2R16?

Bitter taste facilitates the detection of potentially harmful substances and is perceived via bitter taste receptors (TAS2Rs) expressed on the tongue and oral cavity in vertebrates. In primates, TAS2R16 specifically recognizes β-glucosides, which are important in cyanogenic plants' use of cyanide as a feeding deterrent. In this study, we performed cell-based functional assays for investigating the sensitivity of TAS2R16 to β-glucosides in three species of bamboo lemurs ( Prolemur simus, Hapalemur aureus and H. griseus ), which primarily consume high-cyanide bamboo. TAS2R16 receptors from bamboo lemurs had lower sensitivity to β-glucosides, including cyanogenic glucosides, than that of the closely related ring-tailed lemur ( Lemur catta ). Ancestral reconstructions of TAS2R16 for the bamboo-lemur last common ancestor (LCA) and that of the Hapalemur LCA showed an intermediate sensitivity to β-glucosides between that of the ring-tailed lemurs and bamboo lemurs. Mutagenetic analyses revealed that P. simus and H. griseus had separate species - specific substitutions that led to reduced sensitivity. These results indicate that low sensitivity to β-glucosides at the cellular level—a potentially adaptive trait for feeding on cyanogenic bamboo—evolved independently after the Prolemur – Hapalemur split in each species.

Suspected cyanide toxicity in cattle associated with ingestion of laurel - a case report

Background Cyanide is one of the most rapidly acting toxins affecting cattle, with poisoning typically occurring following ingestion of cyanogenic plants. Laurel (Prunus laurocerasus), is one such potentially toxic cyanogenic plant. This case report details fatalities in an Irish herd following the ingestion of laurel and aims to raise awareness of the potential risk that access to laurel hedges poses to farm animals. Case presentation Over a twelve-day period, the death occurred of 36 dairy-cross weanlings; the majority (22 weanlings) died over a two-day period. Two days following entry to a field bounded by a laurel hedge, the weanlings displayed signs of lethargy and profuse green diarrhoea. In the majority of animals there was a limited response to treatment with antimicrobials, vitamin B complex and fluid therapy. Recumbency and death ensued. Cyanosis was noted terminally. Two weanlings were submitted for post mortem examination. Laurel leaves were identified in the rumen contents of one weanling. Post mortem findings and additional test results on cohort animals suggested a number of pathological processes may have been involved in the animals, possibly complicating/exacerbating the effects of laurel ingestion. However, cyanide was considered a factor in a least some of the casualties and arrangements were made to test for cyanide on blood samples from a random selection of seven cohort animals. Although collected one week after exposure to the laurel hedge, toxic cyanide levels were recorded in a sample from one animal, which subsequently died. Conclusions The large fatality rate serves as a timely reminder to include plant poisoning as a differential diagnosis when dealing with large numbers of rapid fatalities. Failure to thoroughly examine rumen contents and collect a detailed history in this case, could easily have allowed death to be attributed to other causes and the involvement of cyanide toxicity to be missed. In cases of individual or group fatalities, history is invaluable and recent entry to new grazing areas or any potential diet change or access to garden plants should be thoroughly investigated.

NATURAL TOXIN SUBSTANCES IN EVERYDAY FOOD

Natural toxins are present in a wide variety of plants. Some of these plants are commonly consumed as food. These toxic substances when ingested in significant amount or when they are not processed appropriately can be potentially harmful to human health causing food poisoning. This study conducted by the Centre for Food Safety of the Food and Environmental Hygiene Department aimed to review natural toxins in food plants commonly consumed in Hong Kong and the measures that can be employed to prevent poisoning from consumption of these food plants. Laboratory study of two natural toxins, glycoalkaloids and cyanogenic glycosides, was carried out to determine the levels of these toxins in food plants commonly consumed in Hong Kong. The effects of preparation and cooking on the reduction of the toxin levels were also studied. Results showed that glycoalkaloid contents varied among the different types of the fresh potatoes tested which ranged from 26-88 mg/kg (average 56 mg/kg). This was within the normal range of glycoalkaloid contents in potatoes of 20 - 100 mg/kg, which JECFA considered that consumptions on a daily basis were not of concern. The highest concentrations of glycoalkaloids were found in potato sprouts. Cyanide was detected in bitter apricot seed, bamboo shoot, cassava, and flaxseed samples in their raw state at levels of 9.3 mg/kg to 330 mg/kg. Cyanide contents were found to be higher in bitter cassava than sweet cassava. Cyanide concentration was found to be highest at the tip portion of bamboo shoot, followed by the middle portion, then the base portion. Cutting cyanogenic food plants into small pieces and cooking them in boiling water reduced cyanide contents of the food commodities by over 90%. Dry heat could not reduce cyanide contents effectively and only reduced around 10% of the cyanide contents in flaxseeds following oven-heating for 15 minutes. Consumers should avoid buying or eating potatoes that show signs of sprouting, greening, physical damage or rotting since glycoalkaloids are not decomposed by cooking. Cutting the cyanogenic plants into smaller pieces and cooking thoroughly in boiling water help release toxic hydrogen cyanide before consumption. When the cooking method chosen is heating under dry-heat or at low moisture contents, limit the intake of the cyanogenic plants to only small amounts. KEY WORDS: glycoalkaloids, cyanogenic

Signaling by hydrogen sulfide and cyanide through post-translational modification

Two cysteine metabolism-related molecules, hydrogen sulfide and hydrogen cyanide, which are considered toxic, have now been considered as signaling molecules. Hydrogen sulfide is produced in chloroplasts through the activity of sulfite reductase and in the cytosol and mitochondria by the action of sulfide-generating enzymes, and regulates/affects essential plant processes such as plant adaptation, development, photosynthesis, autophagy, and stomatal movement, where interplay with other signaling molecules occurs. The mechanism of action of sulfide, which modifies protein cysteine thiols to form persulfides, is related to its chemical features. This post-translational modification, called persulfidation, could play a protective role for thiols against oxidative damage. Hydrogen cyanide is produced during the biosynthesis of ethylene and camalexin in non-cyanogenic plants, and is detoxified by the action of sulfur-related enzymes. Cyanide functions include the breaking of seed dormancy, modifying the plant responses to biotic stress, and inhibition of root hair elongation. The mode of action of cyanide is under investigation, although it has recently been demonstrated to perform post-translational modification of protein cysteine thiols to form thiocyanate, a process called S-cyanylation. Therefore, the signaling roles of sulfide and most probably of cyanide are performed through the modification of specific cysteine residues, altering protein functions.

Spatial separation of the cyanogenic β-glucosidase ZfBGD2 and cyanogenic glucosides in the haemolymph of Zygaena larvae facilitates cyanide release

Low molecular weight compounds are typically used by insects and plants for defence against predators. They are often stored as inactive β-glucosides and kept separate from activating β-glucosidases. When the two components are mixed, the β-glucosides are hydrolysed releasing toxic aglucones. Cyanogenic plants contain cyanogenic glucosides and release hydrogen cyanide due to such a well-characterized two-component system. Some arthropods are also cyanogenic, but comparatively little is known about their system. Here, we identify a specific β-glucosidase ( ZfBGD2) involved in cyanogenesis from larvae of Zygaena filipendulae (Lepidoptera, Zygaenidae), and analyse the spatial organization of cyanide release in this specialized insect. High levels of ZfBGD2 mRNA and protein were found in haemocytes by transcriptomic and proteomic profiling. Heterologous expression in insect cells showed that ZfBGD2 hydrolyses linamarin and lotaustralin, the two cyanogenic glucosides present in Z. filipendulae . Linamarin and lotaustralin as well as cyanide release were found exclusively in the haemoplasma. Phylogenetic analyses revealed that ZfBGD2 clusters with other insect β-glucosidases, and correspondingly, the ability to hydrolyse cyanogenic glucosides catalysed by a specific β-glucosidase evolved convergently in insects and plants. The spatial separation of the β-glucosidase ZfBGD2 and its cyanogenic substrates within the haemolymph provides the basis for cyanide release in Z. filipendulae . This spatial separation is similar to the compartmentalization of the two components found in cyanogenic plant species, and illustrates one similarity in cyanide-based defence in these two kingdoms of life.

Synthesis and Characterization of Hapten-Protein Conjugates for Antibody Production against Cyanogenic Glycosides

Consumption of cyanogenic plants can cause serious health problems for humans. The ability to detect and quantify cyanogenic glycosides, capable of generating cyanide, could contribute to prevention of cyanide poisoning from the consumption of improperly processed cyanogenic plants. Hapten-protein conjugates were synthesized with amygdalin and linamarin by using a novel approach. Polyclonal antibodies were generated by immunizing four New Zealand White rabbits with synthesized amygdalin-bovine serum albumin and linamarin-bovine serum albumin immunogen. This is the first time an antibody was produced against linamarin. Antibody titer curves were obtained from all the four rabbits by using a noncompetitive enzyme-linked immunosorbent assay. High antibody titer was obtained at dilutions greater than 1:50,000 from both immunogens. This new method is an important step forward in preventing ingestion of toxic cyanogenic glycosides.

Cyanogenesis in Lotus and Trifolium species

The occurrence of cyanogenic plants was determined in 48 <i>Trifolium</i> species, 12 <i>Lotus</i> species, in wild population as well as in varieties of <i>T. repens</i> L. and <i>Loins corniculatus</i> L. species. In the genus <i>Trifolium</i> only <i>T. nigrescens</i> Viv. proved to be high-cyanogenic, all the remaining species are acyanogenic or low-cyanogenic. In the <i>T. repens</i> species varieties and wild populations include an insignificant per cent of cyanogenic plants.The genus <i>Lotus</i> comprises both high-cyanogenic and acyanogenic species. In the <i>L. corniculatus</i> species varieties include much more high-cyanogenic plants than do wild populations. It seems that in <i>L. corniculatus</i> the breeding went in a wrong direction, because of lack of plant selection regarding the presence of toxic compounds.

Potential Toxic Levels of Cyanide in Almonds (Prunus amygdalus), Apricot Kernels (Prunus armeniaca), and Almond Syrup

Under normal environmental conditions, many plants synthesize cyanogenic glycosides, which are able to release hydrogen cyanide upon hydrolysis. Each year, there are frequent livestock and occasional human victims of cyanogenic plants consumption. The present work aims to determine the hydrocyanic acid content in different samples of cyanogenic plants, selected from the Tunisian flora, and in the almond syrup. In order to evaluate their toxicity and their impact on the consumer health in the short term as well as in the long term, using the ISO 2164-1975 NT standard, relating to the determination of cyanogenic heterosides in leguminous plants.