Questions and Answers
What are xenobiotics?
Xenobiotics can be both exogenous and endogenous.
True
Describe the role of the liver in detoxification mechanisms.
The liver is the main organ involved in converting xenobiotics to non-toxic, water-soluble forms for excretion.
Phase 1 reactions involve oxidation, reduction, and ______ reactions.
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Match the following conjugation reactions with their corresponding conjugating agents:
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What is the main limiting factor for sulphate conjugation?
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How many types of transferases exist for sulphate conjugation?
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Glutathione conjugation involves a tripeptide as the conjugating agent.
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Cytochrome P450 is present in the smooth ________ of the cell.
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Match the pesticide classification based on mode of entry with their descriptions:
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Study Notes
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Introduction to Xenobiotics
- Xenobiotics or toxicants or drugs or pollutants are substances foreign to the body that can cause changes in structure and functions of an organism
- They get into the body from external sources (not produced within the body) with a few endogenous ones
Types of Xenobiotics
- All therapeutic drugs
- Drug metabolites
- Food additives (coloring, flavors, sweeteners)
- Environmental compounds (pollutants, industrial chemicals)
- Agrochemicals (herbicides, pesticides)
- Cosmetics
Exogenous and Endogenous Xenobiotics
- Exogenous: foreign molecules not normally ingested or utilized by the organism, entering through dietary foodstuffs or in the form of certain medicines/drugs used for therapeutic cause or inhaled through environment
- Endogenous: synthesized in the body or produced as metabolites of various processes in the body, having effects similar to exogenous xenobiotics
Allergy and Its Biochemical Basis
- Allergy: an altered or abnormal tissue reaction, an exaggerated response by certain tissues to some foreign substances, occurring only in hypersensitive people
- Allergic reaction results from contact between a foreign protein called allergen and body tissues that are sensitive to it
- Allergy reactions to substances in food are sometimes spontaneous, peculiar to certain humans, and rarely demonstrable in lower animals
Gastrointestinal Defense System
- The gut is a major immunological organ containing about 10^10 lymphocytes
- Substances surviving the effects of digestive juices and the protective effect of mucous secretion, including the effects of immunoglobulin antibodies, may still be able to penetrate the epithelial barrier of the gut
Detoxification or Biotransformation of Xenobiotics
- Biochemical reactions involved in the conversion of foreign, toxic, or water-insoluble molecules to non-toxic, water-soluble, and excretable forms
- These reactions convert lipophilic to hydrophilic, detoxify, and induce metabolic activation, changing the solubility characteristics of compounds
- The liver is the main organ involved in biotransformation or detoxification reactions due to the presence of various enzymes involved in detoxification processes
Entoxication
- A situation where biotransformation reactions of some xenobiotics conversely increase the toxicity of these compounds
- Example: methanol toxicity, where methanol is metabolized in the liver to formaldehyde and then formic acid, causing metabolic acidosis and damage to the optic nerve
Phase 1 and Phase 2 Reactions
- Phase 1 reactions: oxidation, reduction, and hydrolysis reactions, introducing or exposing a functional group that serves as the active center or point of conjugation for sequential conjugation in a phase II reaction
- Phase 2 reactions: conjugation reactions, making the products of phase 1 reactions more water-soluble and excretable, including glucuronidation, sulphuric acid ester synthesis, hippuric acid synthesis, glutamine conjugation, glutathione conjugation, acetylation, methylation, and thiocyanate synthesis
Factors Affecting Biotransformation of Xenobiotics/Drugs
- Prior administration of the drug or co-administration with other drugs
- Diet
- Hormonal status
- Genetics
- Diseases
- Age and developmental status
- Functional status of liver and kidney
The Biochemical Modes of Action of Pesticides and Herbicides
- Pesticides: substances or mixtures of substances intended for preventing, destroying, repelling, or lessening the damage of any pest
- Herbicides: substances or mixtures of substances intended for preventing, destroying, repelling, or lessening the damage of weeds
Classification of Pesticides
- Classification based on mode of entry: systemic, contact, stomach poisons, fumigants, and repellents
- Classification based on pesticide function and pest organism they kill: insecticides, herbicides, fungicides, rodenticides, and other less well-known pesticides### Classification of Pesticides
- Pesticides can be classified based on their function, such as:
- Growth regulators (stimulate or retard pest growth)
- Defoliants (cause plants to drop leaves)
- Desiccants (speed up plant drying or kill insects)
- Repellents (repel pests)
- Attractants (attract pests, usually to a trap)
- Chemosterilants (sterilize pests)
- Some pesticides can control multiple classes of pests and be classified into more than one category
- Examples of multi-class pesticides include:
- Aldicarb (acaricide, insecticide, and nematicide)
- 2,4-D (herbicide and plant growth regulator)
Classification Based on Chemical Composition
- Chemical composition is a useful method for classifying pesticides
- Pesticides are classified into four main groups based on their chemical composition:
- Organochlorines
- Organophosphorus
- Carbamates
- Pyrethrin and pyrethroids
- Modern pesticides are primarily organic chemicals, including synthetic and plant-based compounds
- Some inorganic compounds are also used as pesticides
Classification Based on Mode of Action
- Pesticides can be classified based on their mode of action, including:
- Physical poison (e.g. activated clay)
- Protoplasmic poison (e.g. Arsenicals)
- Respiratory poison (e.g. Hydrogen cyanide)
- Nerve poison (e.g. Malathion)
- Chitin inhibition (e.g. Diflubenzuron)
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Description
Learn about xenobiotics, substances foreign to the body that can cause changes in structure and functions of an organism, including types such as therapeutic drugs, food additives, and environmental compounds.
