Remco Westerink Neurotoxicology Research Group, Institute for Risk Assessment Sciences
IRAS, what is it? IRAS: Institute for Risk Assessment Sciences (Utrecht University) - Hazard & Exposure => Risk Mission: Education and research into human and veterinary health risks resulting from exposure (environmental, foodrelated, occupational, intentional) to hazardous compounds Biology Pharmaceutical Sciences Veterinary Medicine Medicine NVIC RIVM TNO IRAS Environmental Epidemiology + Veterinary Public Health Toxicology + Veterinary Pharmacology
Exposure Assessment Different fields of toxicology Toxicology & Veterinary Pharmacology Neurotoxicology Endocrine toxicology Immune toxicology Veterinary pharmacology Alternatives in toxicology via mechanism-based in vitro research RISK ASSESSMENT
Neurotoxicology Any form of (compound-induced) dysfunction of the nervous system Pesticides, Persistent environmental pollutants, heavy metals, flame retardants, electromagnetic fields, drugs Tricresyl phosphates! Neurotransmission = intercellular communication
Neurotoxicology Research Group
Aviation safety from a chemical perspective: Tricresyl phosphate (TCP), Aerotoxic syndrome, mechanisms, effects, and biological plausibility Remco Westerink Neurotoxicology Research Group, Institute for Risk Assessment Sciences
Toxic cabin air?
Toxic cabin air?
Toxic cabin air?
Tricresyl phosphates Different isomers: ToCP, TmCP and TpCP, often used as mixture Additive in engine oil/hydrolic fluid Implicated in Aerotoxic Syndrome
Aerotoxic syndrome - Aerotoxic syndrome is a term describing the alleged short-term and long-term adverse health effects that are attributed to exposure to cabin air that has been contaminated with atomized engine oils and other chemicals. - Mainly attributed to tricresyl phosphate (TCP), in particular ToCP, a neurotoxic organophosphate used as lubricant in turbine oil. - Similarity in neurotoxic mechanism of action with organophosporous ester pesticides (parathion etc) and chemical warfare agents (sarin, VX etc) - No formal causal relationship has been established yet
Causality and biological plausibility - Causal relationship: - Confirmed exposure - Multiple physical and chemical factors - Effects - Effective concentrations - Biological plausibility - Sufficient sample size
Exposure: bleed air - Bleed air, contaminated with oil components
Exposure components and incidence - Cabin air is by definition contaminated,.. (ng/m 3 ) TNO measurements of KLM flights - Not only T(o)CP,.. De Ree et al., Neurotoxicology, 2014
Exposure components and incidence - Not only chemical exposure(s), but also physical exposure(s): hypoxia, pressure, radiation, humidity, etc. - Real incidence fume events unknown,..
Exposure and acute effects Acute symptoms - Nausea, diarrhea, vomiting - Breathing difficulties, coughing, irritation of eyes, nose and airways, loss of consciousness - Blurred/tunnel vision, shaking/tremors, loss of balance, impaired movement, seizures Smoke and/or stress-related?
Exposure and chronic effects Chronic symptoms Usually vague! (cf sick building syndrome): - Tired, memory impairment, headache, dizziness, confusion - Blurred/tunnel vision, shaking/tremors, loss of balance, impaired movement Ultimately, incapacitation
Overview of effects Some similarities, but not identical to either OPDIN or painters disease Health problems are real and clinical manifest Abou Donia et al., J. Toxicol. Environment. Health, Part A, (2013)
Plausibility: Mechanisms & acute effects ToCP is an organophosphate: - Inhibition of AChE => excess ACh => increased excitability (transient) => subsequent desensitization of nach-receptors (paralyzing) Usually requires high exposure Acute effects: (mild) cholinergic syndrome including tremor, salivation/urination, reduced heart-rate and gastro-intestinal complaints Symptoms only partly match those of aerotoxic syndrome?
Intermediate syndrome Intermediate syndrome: - OP-induced - 24-96h following (high dose) exposure - Usually muscle weakness, but in severe cases muscle paralysis - Probably under-diagnosed - Often recovery 1-2 weeks Symptoms only partly match those of aerotoxic syndrome? Karalliedde et al., Toxicol Rev (2006)
Plausibility: Mechanisms & chronic effects OP-Induced Delayed Neurotoxicity ( dying back ): - Inhibition of Neuropathy Target Esterase (NTE) - NTE interacts with cytoskeleton, ultimately axonopathy control OPIDN - Usually only upon chronic exposure, possible with single exposure - Occurs weeks after exposure; pain, muscle weakness, paralysis - Symptoms poorly/partly match those of aerotoxic syndrome? Note; can also result from exposure to solvents (n-hexane) Pellin et al., 1988 Jokanovic et al., Clin Neurol Neurosurg (2011)
Plausibility: Mechanisms & chronic effects Chronic OP-Induced Neuropsychiatric disorder (COPIND): - Result of acute poisoning as well as chronic low-dose exposure - Up to 10% (!) of chronic OP exposures!? - Symptoms often vague, include learning/memory, concentration, mood changes, chronic fatigue, tremor, rigidity, etc - Effects delayed (months) and persistent (years) Symptoms match those of aerotoxic syndrome!? Tan et al., Med Hypotheses (2009) Salvi et al., Toxicol Sci (2003) Davies et al., Adv Psychiatr Treat (2000a, b)
More plausibility: genetic risk Organophosphates are metabolized by Cyt P450 to more toxic metabolites. The bioactivated OPs are detoxified by PON-1. PON-1-KO mice are more vulnerable to OPs. OP metabolism (Cyt P450) bioactivated OP metabolism (PON-1) detoxified OP Risk factors: increased CYP activity (more bioactivation), decreased PON-1 activity (less detoxification) Note: PON phenotype not relevant at low OP levels? Coombes et al., Toxicol Lett, 2014 Cole et al., Pharmacogenet Genomics, 2005
Need for action? - Bleed air by definition contaminated - Confirmed exposure - Symptoms of organophosphate poisoning (partly) match aerotoxic syndrome - Risk groups (genetic differences in metabolism) Risk assessment!
Initial TCP Risk Assessment
Step 1
Step 2
Step 3 & 4
Combined step 1-4
More research!
Update TCP Risk Assessment 62.5 ng/kg/d 1.5/62,5 =0,024 ~1.5 ng/kg/d Not 10x ~25x less
Update ToCP Risk Assessment 62.5 ng/kg/d 0.02/62,5 =0,00032 ~0.02 ng/kg/d Not 10x ~2000x less
Causality, plausibility & risk - Exposure? Effects? Biological plausibility? Yes! - TCP Risk?? No! However, organophosphates/tcps may have other actions: - Inhibition of calcium channels (Meijer et al., 2014; 2015) - Increase mitochondrial activity (Duarte et al., 2016) - Reduction neuronal activity (Duarte et al., 2016) - Inhibition glutamatergic signalling (Hausherr et al., 2014; 2016) Yet, so far only at concentrations that are not realistic for human (occupational) exposure Nonetheless, clinical symptoms are real and appear associated with frequent flying Other chemical, physical and psychological causes need to be considered
Cabin air safety: the way forward? Dutch Ministry of Infrastructure & the Environment (I&M): - Hazard characterisation non-ortho TCP isomers Non-ortho isomers slightly less toxic; effects only at high concentrations unrealistic for human exposure European Aviation Safety Agency (EASA): - Oil fumes in realistic exposure scenario (part 1) DG-MOVE (European Union): - Oil fumes in realistic exposure scenario (part 2)
Cabin air safety: integrated readouts Rat cortex: mixed (GABA/glutamate) neuronal cultures with ~45% astrocytes
Cabin air safety: realistic exposure Air-Liquid Interface (ALI) Combined with MEA
Conclusions Risk Assessment: Health effects (very) unlikely due to T(o)CP But clinical symptoms are real so this issue is far from resolved Other chemical causes? ALI-MEA experiments suggest limited risk (oil), but ongoing Further research: Additional exposure assessment Additional endpoints (e.g. Ca 2+ signalling), Repeated and/or prolonged exposure Other chemical/physical agents Other (genetic) risk factors
Thank you for your attention Acknowledgements: Daniel Duarte Joost Rutten Harm Heusinkveld Neurotoxicology Research Group www.neurotoxicology.nl This presentation represents the personal and professional views and opinions of Dr. Remco H.S. Westerink. They do not necessarily reflect those of Utrecht University or our funding bodies (the Dutch Ministry of Infrastructure and the Environment (I&M), the European Aviation Safety Agency (EASA) and DG-MOVE (European Union).
?? Questions?? Acknowledgements: Daniel Duarte Joost Rutten Harm Heusinkveld Neurotoxicology Research Group www.neurotoxicology.nl This presentation represents the personal and professional views and opinions of Dr. Remco H.S. Westerink. They do not necessarily reflect those of Utrecht University or our funding bodies (the Dutch Ministry of Infrastructure and the Environment (I&M), the European Aviation Safety Agency (EASA) and DG-MOVE (European Union).