Directly toxic effects of plant chemicals which may occur in human and animal foods

Low pyrrolizidine alkaloid levels in perennial ryegrass is associated with the absence of a homospermidine synthase gene

BACKGROUND

Pyrrolizidine alkaloids (PAs) are a class of secondary metabolites that function as feeding deterrents in a range of different plant species. In perennial ryegrass (Lolium perenne L.) the only PAs that have been identified are the thesinine-rhamnoside group, which displays significant genetic variation. Homospermidine synthase (HSS) has evolved from deoxyhypusine synthase (DHS) and catalyses the first step in the PA pathway, making it a key candidate for the investigation of genes influencing observed PA trait variation.

RESULTS

During PCR amplification and sequence analysis of DHS we identified two putative HSS genes in perennial ryegrass. One of the genes (LpHSS1) was absent in some perennial ryegrass plants. Thesinine-rhamnoside levels were measured using liquid chromatography coupled with mass spectrometry in a diverse association mapping population, consisting of 693 plants free of fungal endophytic symbionts. Association tests that accounted for population structure identified a significant association of absence of the LpHSS1 gene with lower levels of thesinine-rhamnoside PAs. HSS-like gene sequences were identified for other grass species of the Poaceae, including tall fescue, wheat, maize and sorghum.

CONCLUSION

HSS is situated at the crucial first step in the PA pathway making it an important candidate gene for investigation of involvement in PA phenotypic variation. In this study, PA level in perennial ryegrass was strongly associated with the presence or absence of the LpHSS1 gene. A genetic marker, developed for the presence/absence of LpHSS1, may be used for marker-assisted breeding to either lower or increase PAs in breeding populations of perennial or Italian ryegrass to investigate a potential role in the deterrence of herbivore pests. The presence of HSS-like genes in several other Poaceae species suggests that PA biosynthesis may occur in plant family members beyond perennial ryegrass and tall fescue and identifies a potential route for manipulating PA levels.

Sarcocystis-infection of cattle in Hungary

BACKGROUND

Reports on Sarcocystis-infection of cattle are outdated or lacking in many European countries, including those in the Central-Eastern part of the continent. Therefore, to assess the prevalence of Sarcocystis spp. among bovids in Hungary, a countrywide survey was initiated. In addition, fulminant deaths of four cattle, that showed clinical signs and post mortem lesions resembling acute sarcocystiosis ("Dalmeny disease"), were investigated.

METHODS

During the countrywide survey individual heart and oesophagus samples were collected at slaughterhouses from 151 beef cattle and from 15 buffalo, kept in 31 places of Hungary. Analysis for Sarcocystis spp. was carried out with conventional PCRs for the 18S rDNA gene and gel electrophoresis, followed by sequencing of 36 strongly positive samples. Mortality cases were evaluated by histological, molecular, bacteriological and virological analyses of samples from various organs.

RESULTS

Among slaughtered cattle the rate of Sarcocystis-infection was 66%. S. cruzi was identified as the most prevalent species in aurochs-like breed, and the zoonotic S. hominis in Hungarian grey cattle. Concerning the sudden deaths of cattle, Sarcocystis-infection could not be demonstrated in organs showing haemorrhages, but S. cruzi cysts were present in the muscles. In one case "S. sinensis" was molecularly identified in the blood (indicating sarcocystaemia). Results of analyses for bacterial/viral pathogens were negative.

CONCLUSIONS

S. cruzi appears to be the most prevalent Sarcocystis sp. in cattle in Hungary, followed by the zoonotic S. hominis. However, the rate of infection with both species was shown to differ between cattle breeds. The suspected role of Sarcocystis spp. as causative agents of the fatal cases could not be confirmed.

Toxic phytochemicals and their potential risks for human cancer

Consuming plants for their presumed health benefits has occurred since early civilizations. Phytochemicals are found in various plants that are frequently included in the human diet and are generally thought to be safe for consumption because they are produced naturally. However, this is not always the case and in fact many natural compounds found in several commonly consumed plants are potential carcinogens or tumor promoters and should be avoided.

Considerations on the role of environmental toxins in idiopathic Parkinson's disease pathophysiology

Neurodegenerative diseases are characterized by a progressive dysfunction of the nervous system. Often associated with atrophy of the affected central or peripheral nervous structures, they include diseases such as Parkinson’s Disease (PD), Alzheimer’s Disease and other dementias, Genetic Brain Disorders, Amyotrophic Lateral Sclerosis (ALS or Lou Gehrig’s Disease), Huntington’s Disease, Prion Diseases, and others. The prevalence of neurodegenerative diseases has increased over the last years. This has had a major impact both on patients and their families and has exponentially increased the medical bill by hundreds of billions of Euros. Therefore, understanding the role of environmental and genetic factors in the pathogenesis of PD is crucial to develop preventive strategies. While some authors believe that PD is mainly genetic and that the aging of the society is the principal cause for this increase, different studies suggest that PD may be due to an increased exposure to environmental toxins. In this article we review epidemiological, sociological and experimental studies to determine which hypothesis is more plausible. Our conclusion is that, at least in idiopathic PD (iPD), the exposure to toxic environmental substances could play an important role in its aetiology.

Cycads and their association with certain neurodegenerative diseases

INTRODUCTION

Cycads are ornamental plants that in some parts of the world are used as fresh food or raw material for producing flour with a high nutritional value. However, they also contain active compounds, including methylazoxymethanol, β-methylamino-L-alanine, β-alanine-L-oxalylamino and cycasin, which may produce neurotoxic effects. Some studies have associated consuming cycads and their derivatives with neurodegenerative diseases such as amyotrophic lateral sclerosis/Parkinsonism dementia complex, and other diseases characterised by motor impairment. Therefore, we must not forget that any product, no matter how natural, may present health risks or benefits depending on the chemical compounds it contains and the susceptibility of those who consume it.

DEVELOPMENT

We completed a literature analysis to evaluate the neurotoxic properties of cycads and their association with neurological diseases in order to provide structured scientific information that may contribute to preventing health problems in people who use these plants.

CONCLUSION

Cycads contain neurotoxic compounds that may contribute to the development of neurological diseases when ingested improperly. We must be mindful of the fact that while some plants have a high nutritional value and may fill the food gap for vulnerable populations, they can also be toxic and have a negative impact on health.

Survival and prognostic indicators for cycad intoxication in dogs

BACKGROUND

Cycad palms are commonly used in landscaping and ingestion by dogs can cause disease or death.

OBJECTIVES

Determine the morbidity and case fatality of cycad palm toxicosis in dogs from Louisiana, and examine putative prognostic factors.

ANIMALS

Thirty-four client-owned dogs with confirmed cycad palm toxicosis between 2003 and 2010.

METHODS

Retrospective cohort study. Search of all medical records for animals with cycad palm toxicosis.

RESULTS

Seventeen of 34 (50%) dogs died or were euthanized as a direct consequence of cycad intoxication. There were no differences in presenting signs and physical examination findings between survivors and nonsurvivors. Nonsurvivors had higher serum alanine transaminase activity (median 196 U/L; range 16-4,123 versus 113.5; 48-1,530) and total bilirubin concentration (0.5 mg/dL; 0.1-6.2 versus 0.25; 0-1.7) upon presentation, and their initial serum concentrations of albumin (2.9 g/dL; 1.4-4.1 versus 3.3; 2.2-3.9) were lower than those of survivors. Nadir serum albumin concentration was also lower in nonsurvivors (1.9; 1.4-3.7 versus 3.2; 1.8-3.5). A higher proportion of nonsurvivors had prolonged coagulation times, prothrombin time. and partial thromboplastin time. In a multivariate model, administration of charcoal at initial presentation was associated with longer survival (heart rate [HR] 0.019, 95% CI 0.001-0.644), while high serum aspartate aminotransferase activity was a negative prognostic factor (HR 118.2, 95% CI 2.89-4,826).

CONCLUSIONS AND CLINICAL IMPORTANCE

Cycad intoxication is associated with a higher case fatality than previously published. Several laboratory parameters might help differentiating potential nonsurvivors from survivors. Administration of charcoal as part of the emergency treatment appears to have a protective effect.

Reactions of thiocyanate in the mixture of nitrite and hydrogen peroxide under acidic conditions: Investigation of the reactions simulating the mixture of saliva and gastric juice

Nitrite and SCN(-) in saliva can mixes with H(2)O(2) in the stomach. The mixing can result in the formation of ONOOH. It is not yet known how salivary SCN(-) reacts with ONOOH. An objective of the present study was to elucidate the reaction between ONOOH and SCN(-). In nitrite/H(2)O(2) systems at pH 2, SCN(-) inhibited the consumption of nitrite and the formation of O(3)(-). SCN(-) enhanced the decomposition of ONOOH and H(2)O(2) in HNO(2)/H(2)O(2) systems. Accompanying the reactions, sulfate was formed, suggesting that ONOOH oxidized SCN(-). SCN(-) inhibited the nitration of phenolics induced by HNO(2)/H(2)O(2). The inhibition is discussed taking SCN(-)-dependent reduction of ONOOH to HNO(2) into consideration. SCN(-) also inhibited H(2)O(2)-induced consumption of nitrite and nitration of phenolics in acidified saliva. The result obtained in this study suggests that salivary SCN(-) can reduce ONOOH to O(2)(-)/HNO(2) inhibiting nitrating reactions in the stomach.

Comparison of hepatic in vitro metabolism of the pyrrolizidine alkaloid senecionine in sheep and cattle

OBJECTIVE

To compare hepatic metabolism of pyrrolizidine alkaloids (PAs) between sheep and cattle and elucidate the protective mechanism of sheep.

SAMPLE POPULATION

Liver microsomes and cytosol from 8 sheep and 8 cattle.

PROCEDURE

The PA senecionine, senecionine N-oxide (nontoxic metabolite) and 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP; toxic metabolite) were measured in microsomal incubations. The kcat (turnover number) was determined for DHP and N-oxide formation. Chemical and immunochemical inhibitors were used to assess the role of cytochrome P450s, flavin-containing monooxygenases (FMOs), and carboxylesterases in senecionine metabolism. The CYP3A, CYP2B, and FMO concentrations and activities were determined, in addition to the role of glutathione (GSH) in senecionine metabolism.

RESULTS

DHP concentration did not differ between species. Sheep formed more N-oxide, had higher N-oxide kcat, and metabolized senecionine faster than cattle. The P450 concentrations and isoforms had a large influence on DHP formation, whereas FMOs had a large influence on N-oxide formation. In cattle, CYP3A played a larger role in DHP formation than in sheep. FMO activity was greater in sheep than in cattle. Addition of GSH to in vitro microsomal incubations decreased DHP formation; addition of cytosol decreased N-oxide formation.

CONCLUSIONS AND CLINICAL RELEVANCE

Hepatic metabolism differences alone do not account for the variation in susceptibility seen between these species. Rather, increased ruminal metabolism in sheep appears to be an important protective mechanism, with hepatic enzymes providing a secondary means to degrade any PAs that are absorbed from the rumen.

Gastrointestinally Distributed UDP-glucuronosyltransferase 1A10, Which Metabolizes Estrogens and Nonsteroidal Anti-inflammatory Drugs, Depends upon Phosphorylation

Among gastrointestinal distributed isozymes encoded at the UGT1 locus, UDP-glucuronosyltransferase 1A10 (UGT1A10) metabolizes a number of important chemicals. Similar to broad conversion of phytoestrogens (Basu, N. K., Ciotti, M., Hwang, M. S., Kole, L., Mitra, P. S., Cho, J. W., and Owens, I. S. (2004) J. Biol. Chem. 279, 1429-1441), UGT1A10 metabolized estrogens and their derivatives, whereas UGT1A1, -1A3, -1A7, and -1A8 differentially exhibited reduced activity toward the same. UGT1A10 compared with UGT1A7, -1A8, and -1A3 generally exhibited high activity toward acidic nonsteroidal anti-inflammatory drugs and natural benzaldehyde derivatives, while UGT1A3 metabolized most efficiently aromatic transcinnamic acids known to be generated from flavonoid glycosides by microflora in the lower gastrointestinal tract. Finally UGT1A10, -1A7, -1A8, and -1A3 converted plant-based salicylic acids; methylsalicylic acid was transformed at high levels, and acetylsalicylic (aspirin) and salicylic acid were transformed at moderate to low levels. Atypically UGT1A10 transformed estrogens between pH 6 and 8 but acidic structures preferentially at pH 6.4. Furthermore evidence indicates UGT1A10 expressed in COS-1 cells depends upon phosphorylation; UGT1A10 versus its single, double, and triple mutants at three predicted protein kinase C phosphorylation sites incorporated [(33)P]-orthophosphate and showed a progressive decrease with no detectable label or activity for the triple T73A/T202A/S432G-1A10 mutant. Single and double mutants revealed either null/full activity or null/additive activity, respectively. Additionally UGT1A10-expressing cultures glucuronidated 17beta-[(14)C]estradiol, whereas cultures containing null mutants at protein kinase C sites showed no estrogen conversion. Importantly UGT1A10 in cells supported 10-fold higher glucuronidation of 17beta-estradiol than UGT1A1. In summary, our results suggest gastrointestinally distributed UGT1A10 is important for detoxifying estrogens/phytoestrogens and aromatic acids with complementary activity by UGT1A7, -1A8, -1A3, and/or -1A1 evidently dependent upon phosphorylation.

Pyrrolizidine Alkaloids—Genotoxicity, Metabolism Enzymes, Metabolic Activation, and Mechanisms

Pyrrolizidine alkaloid-containing plants are widely distributed in the world and are probably the most common poisonous plants affecting livestock, wildlife, and humans. Because of their abundance and potent toxicities, the mechanisms by which pyrrolizidine alkaloids induce genotoxicities, particularly carcinogenicity, were extensively studied for several decades but not exclusively elucidated until recently. To date, the pyrrolizidine alkaloid-induced genotoxicities were revealed to be elicited by the hepatic metabolism of these naturally occurring toxins. In this review, we present updated information on the metabolism, metabolizing enzymes, and the mechanisms by which pyrrolizidine alkaloids exert genotoxicity and tumorigenicity.

Differential and special properties of the major human UGT1-encoded gastrointestinal UDP-glucuronosyltransferases enhance potential to control chemical uptake

UDP-glucuronosyltransferase (UGT) isozymes detoxify metabolites, drugs, toxins, and environmental chemicals via conjugation to glucuronic acid. Based on the extended UGT1 locus combined with Northern blot analysis and in situ hybridization, we determined the distribution of UGT1A1 and UGT1A7 through UGT1A10 mRNAs and found them for the first time segmentally distributed in the mucosal epithelia layer of the gastrointestinal tract. Biochemically, recombinant isozymes exhibited pH optima of 5.5, 6.4, 7.6, 8.5, and/or a broad pH range, and activities were found to be unaffected or progressively inhibited by increasing substrate concentrations after attaining Vmax for certain chemicals. Under different optimal conditions, all exhibited wide substrate selections for dietary and environmentally associated chemicals. Evidence also suggests tandem effects of isozymes in the time for completion of reactions when comparing short- and long-term incubations. Moreover, treatment of colon cells with certain diet-associated constituents, curcumin and nordihydroguaiaretic acid, reversibly targets UGTs causing inhibition without affecting protein levels; there is no direct inhibition of control UGT using curcumin as substrate in the in vitro assay. In summary, we demonstrate that UGTs are located in gastrointestinal mucosa, have vast overlapping activities under differential optimal conditions, and exhibit marked sensitivity to certain dietary substrates/constituents, representing a first comprehensive study of critical properties concerning glucuronidating isozymes in alimentary tissues. Additionally, the highly dynamic, complex, and variable properties necessarily impact absorption of ingested chemicals and therapeutic drugs.

Yeast reporter system for rapid determination of estrogenic activity

An in vitro test system for the determination of estrogens, xeno- and phytoestrogens, based on the activation of human estrogen receptor-alpha, has been examined for ability in monitoring environmental estrogens. The system consists of an expression plasmid for the human estrogen receptor-alpha and a reporter plasmid containing the lacZ gene under the control of the vitellogenin hormone response element. These plasmids have been transformed into S. cerevisae. Cultivation of yeast in the presence of estrogenic substances leads to activation of the estrogen receptor and induces the expression of the reporter lacZ. beta-Galactosidase activity of the translated gene lacZ is a measure of the estrogenic activity of a compound. First, the selectivity of the system was compared to data available in the literature. Then the sensitivity of the system was checked. The detection limit is 0.1 ng 17-beta estradiol or an equivalent activity per liter, if a sample can be concentrated 1000-fold. The system has been further characterized by selected compounds with known and unknown estrogenic activity.

The toxicology of African herbal remedies

Toxicity related to traditional medicines is becoming more widely recognized as these remedies become popular in developed countries. Accidental herbal toxicity occurs not only as a result of a lack of pharmaceutic quality control in harvesting and preparation but also because herbal remedies are believed to be harmless. Although there is a huge amount of data available documenting the pharmacologically active ingredients of many plants, it is seldom helpful to the toxicologist in an acute situation. Current analytic methods such as high-performance liquid chromatography, gas chromatography--mass spectrometry, and immunoassays can provide identification of the toxin in those few cases in which the history or symptoms give a clear lead, but broad screening methods remain to be developed. In most cases of plant poisoning, treatment continues to be only of symptoms, with few specific antidotes available. It is important that toxicologists in the West be alert to the possibility of encountering poisoning in patients due to traditional African remedies.

Environmental toxicants and female reproduction

OBJECTIVE

To review current knowledge on the potential effects of environmental toxicants on female reproduction in laboratory animals, wildlife, and humans.

DESIGN

Published literature about the effects of endocrine disruptors, heavy metals, solvents, pesticides, plastics, industrial chemicals, and cigarette smoke on female reproduction.

RESULT(S)

Published data indicate that chemical exposures may cause alterations in reproductive behavior and contribute to subfecundity, infertility, pregnancy loss, growth retardation, intrauterine fetal demise, birth defect, and ovarian failure in laboratory animals and wildlife. Data on the association of chemical exposures and adverse reproductive outcomes in humans are equivocal and often controversial. Some studies indicate that chemical exposures are associated with infertility, spontaneous abortion, or reproductive cancer in women. In contrast, other studies indicate that there is no association between chemical exposures and adverse reproductive outcomes. The reasons for ambiguous findings in human studies are unknown but likely include the fact that many studies are limited by multiple confounders, inadequate methodology, inappropriate endpoints, and small sample size. The mechanism by which chemicals alter reproductive function in all species is complex and may involve hormonal and/or immune disruption, DNA adduct formation, altered cellular proliferation, or inappropriate cellular death.

CONCLUSION(S)

Studies are needed to clarify which toxicants affect human reproduction and by which mechanisms of action. Furthermore, methods should be developed to minimize exposure to known reproductive toxicants such as dioxins and cigarette smoke.