Plant toxicology and risk assessment

Transcription

1 Plant toxicology and risk assessment Anders Permin Head of Department, DVM, PhD

2 Outline The black sheep Examples of plant toxicology What is toxicology? Risk assessment Tox studies Results of tox tests Take home message - conclusion

3 Find the black sheep...

4 Plant Toxicology some examples Apple (Malus domestica) - Seeds are mildly poisonous (amygdalin, a cyanogenic glycoside) it is possible to ingest enough seeds to provide a fatal dose for humans. Cassava (Manihot esculenta) - Roots and leaves contain cyanogenic glucosides (linamarin and lotaustralin). A dose of 40 mg of pure cassava cyanogenic glucoside is sufficient to kill a cow. Cherry (Prunus cerasus), as well as other species (Prunus spp) such as peach (Prunus persica), plum (Prunus domestica), almond (Prunus dulcis), and apricot (Prunus armeniaca). Leaves and seeds contain cyanogenic glycosides. Chocolate. Contains theobromine at levels toxic to dogs and cats. Onions and garlic. Onions and garlic (genus Allium) contain thiosulphate, which in high doses is toxic to dogs, cats and some other livestock.

5 Examples. Potato (Solanum tuberosum). Contain toxic compounds (glycoalkaloids - solanine and chaconine). Wild potatoes can produce toxic effects in humans - headaches, diarrhea and intense digestive disturbances, cramps, weakness and confusion, and in severe cases coma and death. Rhubarb (Rheum rhaponticum). Leaves (oxalic acid - nephrotoxic and corrosive acid). Symptoms of poisoning include kidney disorders, convulsions and coma. Rarely fatal. The LD50 for oxalic acid in rats is about 375 mg/kg body weight (25 grams for a 65 kg human) - 5 kg of the extremely sour leaves would have to be consumed by humans to reach an LD50 of oxalic acid.

6 What is toxicology? What is there that is not a What poison? All things are poison and nothing (is) without poison. Solely the dose determines that a thing is not a poison. Paracelsus ( )

7 Toxicological Risk Assessment In the context of public health, risk assessment is the process of quantifying the probability of a harmful effect to individuals or populations from certain human activities.

8 Toxicological Risk Assessment in 3 steps A question of expected hazards How can a substance harm human beings? Step 1: which adverse effects can be expected? Step 2: what are the critical doses? Step 3: can we establish a safe dose?

9 Toxicological Risk Assessment in 3 steps Step 1: Hazard Identification, aims to determine the qualitative nature of the potential adverse consequences of the contaminant (chemical, radiation, noise, plant, etc.) and the strength of the evidence it can have that effect. This is done, for chemical hazards including plants, by drawing from the results of the sciences of toxicology and epidemiology.

10 Toxicological Risk Assessment in 3 steps Step 2: Hazard Characterisation, determining the relationship between dose and the probability or the incidence of effect. The complexity of this step derives mainly from the need to extrapolate results from experimental animals (e.g. mouse, rat) to humans, and/or from high to lower doses. In addition, the differences between individuals due to genetics or other factors mean that the hazard may be higher for particular groups, called susceptible populations. An alternative to dose-response estimation is to determine an effect unlikely to yield observable effects. In developing such a dose, to account for the largely unknown effects of animal to human extrapolations, increased variability in humans, or missing data, a prudent approach is often adopted by including safety factors in the estimate of the "safe" dose, typically a factor of 10 for each unknown step.

11 Toxicological Risk Assessment in 3 steps Step 3: Exposure Quantification, aims to determine the amount of a contaminant (dose) that individuals and populations will receive. This is done by examining the results of the discipline of exposure assessment. As different location, lifestyles and other factors likely influence the amount of contaminant that is received, a range or distribution of possible values is generated in this step. Particular care is taken to determine the exposure of the susceptible population(s).

12 Exposure

13 Risk Assessment

14 Toxicological studies The risk assessment includes a number of toxicological tests/studies: OECD guidelines ICH guidelines

15 FRET ratio Toxicological studies - drug development NA Purification Libraries/ORFs PCR & RT-PCR qpcr-lux Primers Functional Genomics DNA Cloning -Gateway Molecular Interactions Transfection and Selection Recombinant Protein Expression Gel Electrophoresis / 2D Protein Stains Protein Affinity Purification Inducible shrna Control Reagents Validated Stealth Validated shrna GIBCO Media Sera Stem Cells Process Development BioReliance Genetic Toxicology Mammalian Toxicology Molecular Biology Viral Manufacturing Biopharm Diagnostics Genomics Functional Genomics Proteomics Cell Biology Target ID Validation Assay Development Lead ID Lead Optimization Preclinical Testing Clinical Trials I, II, III Production Labeling & Detection Drug Discovery Bioinformatics Biomarker labeling DNA/RNA/Proteins Antibody labeling In vivo Imaging log [Ligand], M Aldosterone Cortisol Dexamethasone Progesterone Biochemical Targets & Assay Platform Cell-based Assay Tools Compound Screening Capabilities Gene Seq. Analysis Protein Seq. Analysis Gene Profiling: MicroArray Protein Profiling: MicroArray Pathway Analysis Protein Structure Tools

16 Toxicological Studies How can we predict toxic effects and doses without performing experiments on human beings? In vitro studies In vivo studies on animals Epidemiological studies Case studies from accidents Modelling (QSAR)

17 Toxic effects to be studied Acute toxicity by ingestion, dermal application and inhalation Toxicity after repeated exposure Local effects: skin and eyes: corrosive, irritant and sensitizing effects Sensitization by inhalation Effects on reproduction Carcinogenicity Genotoxicity/Mutagenicity

18 Results of tests can be used for deriving NO(A)ELs which in turn can be used for risk assessments by applying uncertainty factors can be used for finding critical effects may give information on mode of action, or mechanism

19 Conclusion: Risk versus Hazard Take home messages: Many plants are poisonous Hazard: the inherent toxicity of an agent Risk: the likelihood of causing adverse effects - completely dependent on exposure Can have minimal risk with highly hazardous agents, and visa-versa