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Physiological factors predisposing to neurotoxicity
1Medical Research Council Toxicology Unit, Leicester, United Kingdom.
Abstract:
Many factors determine individual susceptibility to toxic agents in addition to their primary interaction with the target site. Absorption, delivery to target tissues, bio-activation, bio-inactivation, elimination, and adaptive or protective responses all play important parts in determining the overall response of the individual. In addition changes in the physiological significance of the function which is disrupted may be crucially important. Pulmonary absorption can be limited by ventilation or perfusion, both of which increase with work rate. Tissue uptake can be limited by local blood flow, which is strongly influenced by local functional activity. In areas with a blood-tissue barrier, such as brain and testis, tissue uptake can be strongly influenced by developmental state, protein binding or vascular damage. Metabolic transformation can show marked inter-individual variations at both hepatic and extra-hepatic sites, due to genetic or nutritional influences. The capacity for adaptation to toxicological insult can also vary markedly, depending on functional reserve capacity as well as on inherent plasticity. Examples used to illustrate these factors include: the influence of motor activity on the toxicity of carbon monoxide; of noise on the ototoxicity of aminoglycoside antibiotics; of brain activity on the neurotoxicity of dinitrobenzene; of acid-base balance on the toxicity of nicotine; and of developmental stage on the neurotoxicity of haloperidol. In addition disease states can influence sensitivity. Thus anaemia sensitises to manganese; calcium deficiency to lead; nerve trauma to hexane; and Wilson's disease to copper overload.
Insights
Individual susceptibility to toxic agents depends on absorption, metabolism, and elimination, not just target site interaction. Factors like physiological changes and disease states significantly influence toxicological responses.
Area of Science:
- Toxicology
- Environmental Health
- Pharmacokinetics
Background:
- Individual susceptibility to toxic agents is multifactorial.
- Factors beyond primary target site interaction influence toxicological outcomes.
Purpose of the Study:
- To elucidate the diverse factors influencing individual susceptibility to toxic agents.
- To highlight the importance of pharmacokinetic and physiological variables in toxicology.
Main Methods:
- Review and synthesis of existing toxicological principles.
- Illustration with specific examples of agent-specific toxicities.
Main Results:
- Absorption, distribution, metabolism, and elimination (ADME) critically affect toxicity.
- Physiological factors (e.g., work rate, blood flow) and adaptive responses vary susceptibility.
- Developmental stage, genetic, nutritional, and disease states significantly modify toxic responses.
- Examples include carbon monoxide, aminoglycosides, dinitrobenzene, nicotine, haloperidol, manganese, lead, hexane, and copper.
Conclusions:
- Toxicological outcomes are highly individualized due to complex interactions.
- Understanding these factors is crucial for accurate risk assessment and personalized medicine.