Fungi on Narthecium ossifragum leaves and their possible involvement in alveld disease of Norwegian lambs

Cytotoxic saponins and other natural products from flowering tops of Narthecium ossifragum L

For more than four centuries, the intake of Narthecium ossifragum has been associated with poisoning in domesticated animals. Saponins occurring in flowering tops of the plant are considered to cause kidney damage in calves. At present, there are more than 30 papers on the saponins of N. ossifragum in the literature, although the structures of these compounds have hitherto not been determined. Here, we identify the saponins of N. ossifragum as sarsasapogenin, sarsasapogenin-3-O-β-galactopyranoside, sarsasapogenin-3-O-(2'-O-β-glucopyranosyl-β-galactopyranoside) and sarsasapogenin-3-O-(2'-O-β-glucopyranosyl-3'-O-α-arabinopyranosyl-β-galactopyranoside). Moreover, six aromatic natural products were isolated and characterized from the methanolic extract from flowers of N. ossifragum. Five of these aromatic compounds, chrysoeriol 6-C-β-arabinofuranoside-8-C-β-glucopyranoside, chrysoeriol 6-C-β-arabinopyranosyl-8-C-β-glucopyranoside, chrysoeriol 6-C-β-xylopyranosyl-8-C-β-galactopyranoside, chrysoeriol 6-C-β-galactopyranosyl-8-C-β-glucopyranoside and chrysoeriol 6-C-β-glucopyranosyl-8-C-β-galactopyranoside are undescribed. All compounds were tested for cytotoxicity in mammalian cell lines derived from the heart, kidney, and haematological tissues. The saponins exhibited cytotoxicity in the micromolar range, with proportionally increasing cytotoxicity with increasing number of glycosyl substituents. The most potent compound was the main saponin sarsasapogenin-3-O-(2'-O-β-glucopyranosyl-3'-O-α-arabinopyranosyl-β-galactopyranoside), which produced cell death at concentrations below 3-4 μM in all three cell lines tested. This indicates that the saponins are the toxicants mainly responsible for kidney damage observed in cattle after ingestion of N. ossifragum. Our findings also pave the way for analysis of individual compounds isolated during the biopsies of intoxicated animals.

The aetiology, prevalence and morbidity of outbreaks of photosensitisation in livestock: A review

BACKGROUND

Photosensitisation is a clinical condition occurring in both humans and animals that causes significant injury to affected individuals. In livestock, outbreaks of photosensitisation caused by ingestion of toxic plants are relatively common and can be associated with significant economic loss.

OBJECTIVES

The agents that are most commonly implicated in outbreaks of photosensitisation have not been formally investigated on a global scale. To address this question, a systematic review of the literature was undertaken to determine the most common causative agents implicated in outbreaks of photosensitisation in livestock in Australia and globally, as well as the prevalence and morbidity of such outbreaks.

METHODS

A systematic database search was conducted to identify peer-reviewed case reports of photosensitisation in livestock published worldwide between 1900 and April 2018. Only case reports with a full abstract in English were included. Non peer-reviewed reports from Australia were also investigated. Case reports were then sorted by plant and animal species, type of photosensitisation by diagnosis, location, morbidity and mortality rate and tabulated for further analysis.

RESULTS

One hundred and sixty-six reports qualified for inclusion in this study. Outbreaks were reported in 20 countries. Australia (20), Brazil (20) and the United States (11) showed the highest number of peer-reviewed photosensitisation case reports from this analysis. Hepatogenous (Type III) photosensitisation was the most frequently reported diagnosis (68.5%) and resulted in higher morbidity. Panicum spp., Brachiaria spp. and Tribulus terrestris were identified as the most common causes of hepatogenous photosensitisation globally.

CONCLUSIONS

Hepatogenous photosensitisation in livestock represents a significant risk to livestock production, particularly in Australia, Brazil, and the United States. Management of toxic pastures and common pasture weeds may reduce the economic impact of photosensitisation both at a national and global level.

Toxic aromatic compounds from fruits of Narthecium ossifragum L

The intake of Narthecium ossifragum, commonly known as bog asphodel, has been associated with toxic effects observed in sheep for centuries. Although the plant has been studied for five centuries little is known about its chemical constituents. Six previously undescribed natural products, naringenin(3 → 6″)luteolin, naringenin(3 → 6″)chrysoeriol, liovil 4-O-β-glucopyranoside, 2,6-dimethoxy cinnamic acid, (E)-4-(3-hydroxy-2,2-dimethylchroman-6-yl)but-3-en-2-one and (E)-4-(4-(((E)-4-hydroxy-3-methylbut-2-en-1-yl)oxy)phenyl)but-3-en-2-one, have been identified from fruits of N. ossifragum for the first time. In addition, the rare natural product 4-hydroxy-3-(3-methylbut-2-enyl)benzaldehyde and the five known compounds 4-hydroxycinnamic acid, quercetin 3,3'-dimethyl ether, quercetin 3,7-dimethyl ether, chrysoeriol 7-O-β-glucopyranoside and the di-C-glycosylflavone isoschaftoside were all characterized for the first time from the fruits of N. ossifragum. The discovery of sufficient amounts of 4-hydroxy-3-(3-methylbut-2-enyl)benzaldehyde in fresh plant material of N. ossifragum to allow complete structure elucidation by NMR and HRMS supports the possibility that fungi associated with N. ossifragum may be able to produce enough toxins to play a significant role in the pathogenicity of N. ossifragum. 4-Hydroxy-3-(3-methylbut-2-enyl)benzaldehyde showed mild toxicity towards normal rat kidney (NRK) and more profound activity towards MOLM13 acute myeloid leukemia cells (IC₅₀ = 430 μM and 68 μM, respectively). Naringenin(3 → 6″)luteolin had IC₅₀ of 230 μM towards NRK cells, and 115 μM towards MOLM13 cells. Microscopic evaluation suggests that these two compounds induce cell death by different mechanisms.

Photosensitisation of livestock grazing Narthecium ossifragum: Current knowledge and future directions

Photosensitisation diseases can cause production and animal welfare losses world-wide. In North-West Europe a photosensitisation disease complex known as 'plochteach', 'yellowses', 'saut' and 'alveld' occurs in lambs on extensive pastures containing bog asphodel (Narthecium ossifragum). Affected lambs develop lesions on the ears, face and sometimes the back, with erythema, oedema, ulceration and necrosis that can be followed by secondary infection and death. Adult sheep appear unaffected, the incidence in lambs varies from year to year and there are variations in susceptibility between- and within-breeds. The definitive cause remains uncertain although ingestion of N. ossifragum, which contains hepatotoxic saponins, has been implicated in the aetiology. However, problems replicating the disease complex by feeding N. ossifragum in a controlled environment have led to alternative hypotheses, including possible intake of toxins from fungal spores and cyanobacteria. Further research is required to assess the putative role of N. ossifragum, the scale of economic and animal welfare losses associated with the disease, how best to identify affected animals before external clinical signs appear and the treatment and management of clinical cases. Given the challenges involved in isolating the causative agent(s) of plochteach, an animal breeding route may be effective if heritability of resistance/susceptibility can be demonstrated.

Molecular characterization and evaluation of plant litter-associated fungi from the spring ‘grazing corridor’ of a sheep herd vulnerable to alveld disease

This study sample and identify species of fungi on withered vegetation in the spring 'grazing corridor' from infields to Narthecium bogs for a sheep herd almost chronically vulnerable to phototoxic disease. Hepatogen photosensitizing disorders like alveld attack grazing sheep, especially lambs, in various parts of the world. It has been hypothesized that saponin metabolites in the monocotyledonous plant Narthecium ossifragum causes the disorder in Norway, however, this has not been verified. Thus, the search for other causal agents or saponin cofactors (the cofactor hypothesis) has been intensified, and endophytic poisonous fungi associated with dead N. ossifragum leaves and grasses are among the prime suspects. The fungal diversity was targeted by obtaining axenic cultures from surface-sterilized plant material, with subsequent DNA isolation, PCR, and sequencing of the ITS nrDNA region. The taxonomic affinities of the obtained sequences were thereafter explored by similarity searches against the public access sequence database EMBL/GenBank/DDBJ. Among the spectrum of identified taxa were representatives of Cladosporium, Fusarium, Penicillium, and Trichoderma, all of which are well known as potential producers of toxins. A possible involvement of these toxic species in the etiology of alveld is evaluated and discussed.

Sapogenin levels in Narthecium ossifragum plants and Ovis aries lamb faeces during two alveld outbreaks in Møre og Romsdal, Norway, 2001

The proposal that saponins produced by the lily bog asphodel (Narthecium ossifragum) may be the direct cause of the hepatogenous photosensitization disease alveld seen in Norwegian lambs was investigated by comparing sapogenin levels in two control and two toxic pastures, and in faeces from lambs grazing the four pastures in the Halsa and Surnadal municipalities, Møre og Romsdal county, Norway. Generally similar levels of sapogenins, determined after hydrolysis of parent plant saponins, were found in Narthecium leaves collected in June/July 2001 from the two alveld outbreak areas and two nearby control areas. Differences in the median sapogenin levels determined for leaf samples in outbreak and control areas were not statistically significant. The total level of free and conjugated sapogenins in faeces recovered from the rectums of lambs grazing the outbreak and control pastures areas varied greatly. The results obtained do not support the hypothesis that a dose-response relationship exists between Narthecium saponin levels and the occurrence of alveld outbreaks.

Summer variation in the concentration of steroidal sapogenins in and the degree of fungal infection on Narthecium ossifragum plants from Møre og Romsdal County, Norway

Thirty-nine leaf samples of Narthecium ossifragum collected from eight sites in Møre og Romsdal County, Norway, during June-September 1997 and 41 leaf samples collected at five sites in the same county during June-August 1998 were analysed for the concentrations of steroidal sapogenins using GC-MS. The 1998 samples were also examined for fungal elements (conidia and hyphae) after incubation in a moist chamber for 10-14 days. The highest 1997 and 1998 leaf sapogenin concentrations (4881 and 7115 mg/kg dry matter, respectively) were 13-14 times greater than the lowest sapogenin concentrations found (344 and 531 mg/kg dry matter, respectively). The results did not reveal systematic differences in sapogenin concentrations between the two seasons, or between samples harvested early or late in the same seasons, or between sapogenin concentrations in plants harvested at different sites. Cladosporium magnusianum was the predominant fungus found in the samples. The degree of fungal infection on the samples was in generally low, but the number of C. magnusianum colonies in the moist chamber preparations and fungal elements (conidia and hyphae) in leaf washings and on leaves tended to increase with time. Factor analysis and multiple regression analysis performed on the chemical and fungal results suggest that sporulation may have occurred in the fungi in response to increase in sapogenin concentrations.

An experimental investigation of the effects of nitrogen deposition to Narthecium ossifragum

Narthecium ossifragum (L.) Hudson was subjected to artificial deposition events in three experiments. In the first, a laboratory experiment, 1.0 m nitrate significantly decreased the growth of Narthecium, and the shoot and root nitrogen content of the plants was increased in all enhanced nitrogen treatments. In the second experiment, solutes were applied in situ to a relatively unpolluted upland ombrotrophic mire at concentrations measured in cloud water at a polluted site in England. There was no effect on Narthecium tissue nitrogen concentration due to either ammonium or nitrate applied alone but the shoot nitrogen was significantly increased when the ammonium and nitrate were applied in combination. In the third experiment, a piece of upland ombrotrophic mire from a relatively unpolluted site in North Wales was transplanted to a polluted site in northern England. After two years both the shoots and roots of Narthecium present in the mire showed a higher nitrogen concentration in the transplant compared with the control. These data show that nitrogen supply in the southern Pennines is supra-optimal for Narthecium, which implies that in such situations it (and other species with a similar ecological strategy) would be out-competed by more vigorous species. The data from the field experiment at the relatively unpolluted site imply that even there, nitrogen supply is close to supra-optimal for Narthecium.