A new, very sensitive method of assessment of ptaquiloside, the major bracken carcinogen in the milk of farm animals

Cross-species oncogenomics offers insight into human muscle-invasive bladder cancer

BACKGROUND

In humans, muscle-invasive bladder cancer (MIBC) is highly aggressive and associated with a poor prognosis. With a high mutation load and large number of altered genes, strategies to delineate key driver events are necessary. Dogs and cats develop urothelial carcinoma (UC) with histological and clinical similarities to human MIBC. Cattle that graze on bracken fern also develop UC, associated with exposure to the carcinogen ptaquiloside. These species may represent relevant animal models of spontaneous and carcinogen-induced UC that can provide insight into human MIBC.

RESULTS

Whole-exome sequencing of domestic canine (n = 87) and feline (n = 23) UC, and comparative analysis with human MIBC reveals a lower mutation rate in animal cases and the absence of APOBEC mutational signatures. A convergence of driver genes (ARID1A, KDM6A, TP53, FAT1, and NRAS) is discovered, along with common focally amplified and deleted genes involved in regulation of the cell cycle and chromatin remodelling. We identify mismatch repair deficiency in a subset of canine and feline UCs with biallelic inactivation of MSH2. Bovine UC (n = 8) is distinctly different; we identify novel mutational signatures which are recapitulated in vitro in human urinary bladder UC cells treated with bracken fern extracts or purified ptaquiloside.

CONCLUSION

Canine and feline urinary bladder UC represent relevant models of MIBC in humans, and cross-species analysis can identify evolutionarily conserved driver genes. We characterize mutational signatures in bovine UC associated with bracken fern and ptaquiloside exposure, a human-linked cancer exposure. Our work demonstrates the relevance of cross-species comparative analysis in understanding both human and animal UC.

Evaluation and Monitoring of the Natural Toxin Ptaquiloside in Bracken Fern, Meat, and Dairy Products

Ptaquiloside, a naturally occurring cancer-causing substance in bracken fern, has been detected in the meat and milk of cows fed a diet containing bracken fern. A rapid and sensitive method for the quantitative analysis of ptaquiloside in bracken fern, meat, and dairy products was developed using the QuEChERS method and liquid chromatography-tandem mass spectrometry. The method was validated according to the Association of Official Analytical Chemists guidelines and met the criteria. A single matrix-matched calibration method with bracken fern has been proposed, which is a novel strategy that uses one calibration for multiple matrices. The calibration curve ranged from 0.1 to 50 µg/kg and showed good linearity (r² > 0.99). The limits of detection and quantification were 0.03 and 0.09 µg/kg, respectively. The intraday and interday accuracies were 83.5-98.5%, and the precision was <9.0%. This method was used for the monitoring and exposure assessment of ptaquiloside in all routes of exposure. A total of 0.1 µg/kg of ptaquiloside was detected in free-range beef, and the daily dietary exposure of South Koreans to ptaquiloside was estimated at up to 3.0 × 10^-5 µg/kg b.w./day. The significance of this study is to evaluate commercially available products in which ptaquiloside may be present, to monitor consumer safety.

Food-Borne Chemical Carcinogens and the Evidence for Human Cancer Risk

Commonly consumed foods and beverages can contain chemicals with reported carcinogenic activity in rodent models. Moreover, exposures to some of these substances have been associated with increased cancer risks in humans. Food-borne carcinogens span a range of chemical classes and can arise from natural or anthropogenic sources, as well as form endogenously. Important considerations include the mechanism(s) of action (MoA), their relevance to human biology, and the level of exposure in diet. The MoAs of carcinogens have been classified as either DNA-reactive (genotoxic), involving covalent reaction with nuclear DNA, or epigenetic, involving molecular and cellular effects other than DNA reactivity. Carcinogens are generally present in food at low levels, resulting in low daily intakes, although there are some exceptions. Carcinogens of the DNA-reactive type produce effects at lower dosages than epigenetic carcinogens. Several food-related DNA-reactive carcinogens, including aflatoxins, aristolochic acid, benzene, benzo[a]pyrene and ethylene oxide, are recognized by the International Agency for Research on Cancer (IARC) as causes of human cancer. Of the epigenetic type, the only carcinogen considered to be associated with increased cancer in humans, although not from low-level food exposure, is dioxin (TCDD). Thus, DNA-reactive carcinogens in food represent a much greater risk than epigenetic carcinogens.

Ptaquiloside and Pterosin B Levels in Mature Green Fronds and Sprouts of Pteridium arachnoideum

Pteridium arachnoideum, a fern of the Pteridium aquilinum species complex found in South America, is responsible for several different syndromes of poisoning. Cases of bovine enzootic hematuria and upper alimentary squamous cell carcinoma are both frequent occurrences in Brazil, whereas only bovine enzootic hematuria is noted with any frequency around the world. The reason for the high frequency of upper alimentary squamous cell carcinoma in Brazil is not currently known. One possible explanation may be the higher levels of ptaquiloside and pterosin B in Brazilian Pteridium than those present in the plant in other countries. However, these levels have not yet been determined in P. arachnoideum. Thus, the present study aimed to measure and compare ptaquiloside and pterosin B levels in mature green fronds and sprouts of P. arachnoideum collected from different locations in Brazil. Samples of P. arachnoideum were collected from the states of Minas Gerais and Rio Grande do Sul. A total of 28 mature leaf samples and 23 sprout samples were used. The mean concentrations of ptaquiloside and pterosin B present in the mature green fronds of P. arachnoideum ranged from 2.49 to 2.75 mg/g and 0.68 to 0.88 mg/g, respectively; in P. arachnoideum sprouts, mean concentrations of ptaquiloside and pterosin B ranged from 12.47 to 18.81 mg/g, and 4.03 to 10.42 mg/g for ptaquiloside and pterosin B, respectively. Thus, ptaquiloside and pterosin B levels in P. arachnoideum samples collected in Brazil were higher in sprouts than in mature green fronds, as observed in other countries. However, there was no variation in ptaquiloside levels among plants collected from different cities in Brazil. The high frequency of upper alimentary squamous cell carcinoma in Brazilian cattle may not be attributed to greater levels of ptaquiloside and pterosin B in P. arachnoideum than in other Pteridium species in other countries.

Fate of ptaquiloside-A bracken fern toxin-In cattle

Ptaquiloside is a natural toxin present in bracken ferns (Pteridium sp.). Cattle ingesting bracken may develop bladder tumours and excrete genotoxins in meat and milk. However, the fate of ptaquiloside in cattle and the link between ptaquiloside and cattle carcinogenesis is unresolved. Here, we present the toxicokinetic profile of ptaquiloside in plasma and urine after intravenous administration of ptaquiloside and after oral administration of bracken. Administered intravenously ptaquiloside, revealed a volume of distribution of 1.3 L kg-1 with a mean residence-time of 4 hours. A large fraction of ptaquiloside was converted to non-toxic pterosin B in the blood stream. Both ptaquiloside and pterosin B were excreted in urine (up to 41% of the dose). Oral administration of ptaquiloside via bracken extract or dried ferns did not result in observations of ptaquiloside in body fluids, indicating deglycosolidation in the rumen. Pterosin B was detected in both plasma and urine after oral administration. Hence, transport of carcinogenic ptaquiloside metabolites over the rumen membrane is indicated. Pterosin B recovered from urine counted for 7% of the dose given intravenously. Heifers exposed to bracken for 7 days (2 mg ptaquiloside kg-1) developed preneoplastic lesions in the urinary bladder most likely caused by genotoxic ptaquiloside metabolites.

Revisiting an old disease? Risk factors for bovine enzootic haematuria in the Kingdom of Bhutan

Bovine enzootic haematuria (BEH) is a debilitating disease of cattle caused by chronic ingestion of bracken fern. Control of BEH is difficult when bracken fern is abundant and fodder resources are limited. To fill a significant knowledge gap on modifiable risk factors for BEH, we conducted a case-control study to identify cattle management practices associated with BEH in the Bhutanese cattle population. A case-control study involving 16 of the 20 districts of Bhutan was carried out between March 2012 and June 2014. In Bhutan sodium acid phosphate and hexamine (SAP&H) is used to treat BEH-affected cattle. All cattle greater than three years of age and treated with SAP&H in 2011 were identified from treatment records held by animal health offices. Households with at least one SAP&H-treated cattle were defined as probable cases. Probable case households were visited and re-classified as confirmed case households if the BEH status of cattle was confirmed following clinical examination and urinalysis. Two control households were selected from the same village as the case household. Households were eligible to be controls if: (1) householders reported that none of their cattle had shown red urine during the previous five years, and (2) haematuria was absent in a randomly selected animal from the herd following clinical examination. Details of cattle management practices were elicited from case and control householders using a questionnaire. A conditional logistic regression model was used to quantify the association between exposures of interest and household BEH status. A total of 183 cases and 345 controls were eligible for analysis. After adjusting for known confounders, the odds of free-grazing for two and three months in the spring were 3.81 (95% CI 1.27-11.7) and 2.28 (95% CI 1.15-4.53) times greater, respectively, in case households compared to controls. The odds of using fresh fern and dry fern as bedding in the warmer months were 2.05 (95% CI 1.03-4.10) and 2.08 (95% CI 0.88-4.90) times greater, respectively, in cases compared to controls. This study identified two husbandry practices that could be modified to reduce the risk of BEH in Bhutanese cattle. Avoiding the use of bracken fern as bedding is desirable, however, if fern is the only available material, it should be harvested during the colder months of the year. Improving access to alternative fodder crops will reduce the need for householders to rely on free-grazing as the main source of metabolisable energy for cattle during the spring.

Dissipation of pterosin B in acid soils - Tracking the fate of the bracken fern carcinogen ptaquiloside

Bracken ferns (Pteridium spp.) are well-known for their carcinogenic properties, which are ascribed to the content of ptaquiloside and ptaquiloside-like substances. Ptaquiloside leach from the ferns and may cause contamination of drinking water. Pterosin B is formed by hydrolysis of ptaquiloside. In soil, Pterosin B is adsorbed more strongly and it is expected to have a slower turnover than ptaquiloside. We thus hypothesized that pterosin B may serve as an indicator for any past presence of ptaquiloside. Pterosin B degradation was studied in acid forest soils from bracken-covered and bracken-free areas. Soil samples were incubated with pterosin B at 3 and 8 μg g^-1 for 10 days, whereas sterile (autoclaved) samples were incubated for 23 days. Pterosin B showed unexpected fast degradation in soils with full degradation in topsoils in 2-5 days. Pterosin B dissipation followed the sum of two-first order reactions. The initial fast reaction with half-lives of 0.7-3.5 h contributed 11-59% of the total pterosin B degradation, while the slow reaction was 20-100 times slower than the fast reaction. Total dissipation half-lives were shorter for loamy sand (4 h) than for sandy loam soils (28 h). No degradation of pterosin B took place under sterile conditions assuming observed dissipation during the first 3 h could be attributed to irreversible sorption. Our results demonstrate that pterosin B is microbially degraded and that pterosin B is as unstable as ptaquiloside and hence cannot be used as an indicator for former presence of ptaquiloside in soil.

Ptaquiloside, the major carcinogen of bracken fern, in the pooled raw milk of healthy sheep and goats: an underestimated, global concern of food safety

Bracken fern (Pteridium aquilinum) is a worldwide plant containing toxic substances, which represent an important chemical hazard for animals, including humans. Ptaquiloside, 1, a norsesquiterpenoid glucoside, is the major carcinogen of bracken detected in the food chain, particularly in the milk from farm animals. To date, ptaquiloside has been shown in the milk of cows feeding on a diet containing bracken fern. This is the first study that shows the systematic detection of ptaquiloside, 1, and reports its direct quantitation in pooled raw milk of healthy sheep and goats grazing on bracken. Ptaquiloside, 1, was detected by a sensitive method based on the chemical conversion of ptaquiloside, 1, into bromopterosine, 4, following gas chromatography-mass spectrometry (GC-MS) analysis. The presence of ptaquiloside, 1, possibly carcinogenic to humans, in the milk of healthy animals is an unknown potential health risk, thus representing a harmful and potential global concern of food safety.

Ptaquiloside in Pteridium aquilinum subsp. aquilinum and corresponding soils from the South of Italy: influence of physical and chemical features of soils on its occurrence

The bracken fern Pteridium aquilinum (L.) Kuhn, one of the most common plant species on Earth, produces a wide range of secondary metabolites including the norsesquiterpene glucoside ptaquiloside (PTA). Several studies are present in literature about eco-toxicological aspects related to PTA, whereas results about the effect of growth conditions and soil properties on the production and mobility of PTA are sometimes conflicting and further investigations are needed. The aim of the present work is to investigate the occurrence and possible fate of PTA in soils showing different physical and chemical features, and collected in several areas of the South of Italy. The PTA content was determined in both soil and fern samples by GC-MS; both the extraction protocol and recovery were previously tested through incubation studies. Soils samples were also characterized from the physical and chemical points of view in order to correlate the possible influence of soil parameters on PTA production and occurrence. PTA concentration in P. aquilinum fern seemed to be significantly affected by the availability of nutrients (mainly P) and soil pH. At the same time, PTA concentration in soil samples was always undetectable, independent of the PTA concentration in the corresponding Pteridium samples and pedo-climatic conditions. This seems to suggest the degradation of the PTA by indigenous soil microbial community, whereas incubation studies underlined a certain affinity of PTA for both organic colloids and clay/silt particles.

Influence of bracken fern (Pteridium caudatum L. Maxon) pre-treatment on extraction yield of illudane glycosides and pterosins

INTRODUCTION

Bracken (Pteridium spp) illudane glycosidess are labile biologically active terpenoids that undergo decomposition in mild alkali or acid, heat and enzymatic reactions. Hypothetically, quantitation of these weakly chromophoric carcinogens may be challenged by plant sample preparation procedures that may alter the yield of isolates.

OBJECTIVE

To study the influence of common plant sample pre-treatments on the recovery of Pteridium caudatum illudane glycoside carcinogens, ptaquiloside (1a), caudatoside (1c) and ptaquiloside Z (1d), and associated pterosins A, B and Z (2a, b, c) using HPLC-DAD.

METHOD

Bracken fronds were divided in equal left/right sections. One section was subjected to high vacuum desiccation (VD) and the other to freeze-drying (FD), air drying at room temperature (AD) for 7 days, air drying at 70 °C for 72 h (HD), or no treatment (fresh frond, FF). Quantitation was achieved by brief hot-water extraction, base-acid transformation of 1a, 1c and 1d to 2a, b, c and HPLC-DAD analysis against standards.

RESULTS

Substantial differences in extraction yields were found for all illudane glycosides in the order FF > FD ≈ VD > AD > HD. Illudane instability to HD was 1c > 1d > 1a. Significant losses also were recorded in yields of Pterosins A, B and Z.

CONCLUSION

Glycoside extraction suffers from substantial yield loss of all illudane glycosides and indigenous pterosins in all sample pre-treatments studied relative to fresh frond material.

Bracken-associated human and animal health hazards: chemical, biological and pathological evidence

Bracken (Pteridium aquilinum) is a widely distributed carcinogenic fern, to whose toxins human populations are exposed through multiple routes. Animals are also affected by bracken toxins, leading to serious production losses yearly. Accordingly, several governmental reports regarding the safeguard of public health against bracken carcinogens have been recently issued. This review describes the main bioactive compounds identified in bracken and their biological effects at the molecular, cellular, pathological and populational levels, with particular emphasis on ptaquiloside, the main bracken carcinogen. Recent biopathological studies shedding further light on the genotoxicity immunotoxicity and carcinogenicity of ptaquiloside are discussed. Key steps on the long effort to understand bracken toxicology are also reviewed, along with the latest findings on new bracken toxins and human exposures routes. The presence of ptaquiloside and related terpene glycosides in milk, meat and water are of particular concern from the viewpoints of both human and animal health.