- Slides: 50
Toxicity and Human Health Inneke Hantoro
Toxicity is the potential of a chemical to induce an adverse effect in a living organism e. g. , man. How a toxicant enters an organism Toxicity How it interacts with target molecule How organism deals with the insult
The induction of toxic effects largely depends on the disposition of the substances concerned. Interaction of a substance with a living organism Kinetic Phase absorption, distribution, metabolism, and excretion the fate of substance in the body has a number of defense mechanisms at various levels of the kinetic phase, metabolism & excretion Dynamic Phase interactions of the toxicant within the organism and describes processes at organ, tissue, cellular, and molecular levels
Potential stages in the development of toxicity after chemical exposure Toxicant Delivery Interaction with target molecule Alteration of biological environment Cellular dysfunction, injury Dysrepair Klassen (2001) T O X I C I T Y
Step 1: Delivery Theoretically, the intensity of a toxic effect depends primarily on the concentration and persistence of the ultimate toxicant at its site of action. The ultimate toxicant is the chemical species that reacts with the endogenous target molecule (e. g. , receptor, enzyme, DNA, protein, lipid) or critically alters the biological (micro) environment, initiating structural and/or functional alterations that result is toxicity.
Factors that can facilitate the accumulation of ultimate toxicants
Absorption is the transfer of a chemical from the site of exposure, usually an external or internal body surface (e. g. , skin, mucosa of the alimentary and respiratory tracts), into the systemic circulation. Presystemic Elimination During transfer from the site of exposure to the systemic circulation, toxicants may be eliminated.
Distribution to and away from the target Mechanisms facilitating distribution to a target: the porosity of the capillary endothelium specialized membrane transport accumulation in cell organelles reversible intracellular binding
Mechanisms Opposing Distribution to a Target Distribution of toxicants to specific sites may be hindered by several processes, including: binding to plasma proteins specialized barriers distribution to storage sites such as adipose tissue association with intracellular binding proteins export from cells
Excretion is the removal of xenobiotics from the blood and their return to the external environment. Reabsorbtion.
Toxication Biotransformation to harmful products is called toxication or metabolic activation. With some xenobiotics, toxication confers physicochemical properties that adversely alter the microenvironment of biological processes or structures. For example, oxalic acid formed from ethylene glycol may cause acidosis and hypocalcaemia as well as obstruction of renal tubules by precipitation as calcium oxalate.
Detoxication Biotransformation that eliminates an ultimate toxicant or prevents its formation is called detoxication.
The absorption of toxicants Process by which the toxicants cross the epithelial cell barriers. Route of absorption: Skin Respiratory Digestive
The absorption of toxicants Absorption through skin, lung or intestinal tissue is followed by passage into the interstitial fluid. Interstitial fluid (15%), intracellular fluid (40%), blood plasma (8%) Toxicants is absorbed & enters the lymph or blood supply and is mobilized to other parts of the body. Toxicant can enter local tissue cells.
Integumentary System Route Skin, hair, nails, mammary glands. Skin is the largest organ in the body. Epidermis. – Avascular, keratinized stratum corneum, 1520 cells thick, provides most toxicant protection. Dermis. – Highly vascularized; nerve endings, hair follicles, sweat and oil glands. Hypodermis. – Connective and adipose tissue.
Respiratory System Route Skin: stratified squamous epithelial tissue Respiratory system: squamous epithelium, cilated columnar and cuboidal epithelium Non-keratinized, but cilated tissues and muscus-secreting cells provide “mucociliary escalator”
Nasopharyngeal. – Nostrils, nasopharynx, oropharynx, laryngopharynx. – Hairs and mucus; trap >5 μm particulates. Tracheobronchial. – Trachea, bronchioles; cillial action. – Luminal mucus aerosols and gases. Pulmonary – Alveoli - high surface area gas exchange with cardiovascular system.
Digestive System Route Mouth, oral cavity, esophagus, stomach, small intestine, rectum, anus. Residence time can determine site of toxicant entry/injury. – Mouth (short); small intestine (long). – Absorption of toxicants can take place anywhere, but much of the tissue structure in the digestion system is specially designed for absorption.
Digestive System Route Tissue differentiation. Mucosa – Avascular, s. squamus or columnar epithelium. – In some regions villi and microvilli structure aids in absorption (high surface area). Submucosa – Blood, lymph system interface. Muscularis (movement). Serosa (casing).
Distribution of toxicants in the body Lymphatic system Lymph capillaries, nodes, tonsils, spleen, thymus, lymphocytes Drain fluids from systems Slow circulation Cardiovascular system Heart, arterial and venous vessels, capillaries, blood Fast circulation Major distribution by blood
In blood system, major toxicant transport medium: Erythrocytes (red blood cell) § Leukocytes (white blood cell) § Platelets (thrombocytes) § Plasma (non-cellular fluid) §
Factors affecting Distribution: Physical or chemical properties of toxicants Concentration gradient (volume of distribution) Cardiac output to the specific tissues Detoxication reactions (protein binding) Tissue sensitivity to the toxicant (adipose tissue, receptors) Barriers that inhibit migration (bloodbrain, placental)
Step 2: Reaction of toxicants with the target molecule
Step 3: alteration of the regulatory or maintenance function of the cell
Storage of toxicants Accumulation of toxicants in specific tissues. Binding to plasma proteins. Albumin most abundant and common binder Storage in bones. Heavy metals, like Pb Storage in liver. Blood flow, biotransformation Storage in the kidneys. Storage in fat. Lipophilic compounds
Target Organ Toxicity Adverse effects or disease states manifested in specific organs in the body High cardiac output = higher exposure Organs each have specialized tissues and cells Differentiated cellular processes and receptors Toxicants and metabolites may have specific reactive pathways
Target Organ Toxicity Toxicants do not affect all organs to the same extent A toxicant may have several sites of action and target organs Multi-toxicant exposure may target the same organ The target organ may not be the site for storage
The main target organs for the systemic toxicity of xenobiotics are: Skin, mucous membrane Lungs Liver, kidney Bone marrow Immune system Nervous system (central & peripheral) Cardiovascular system Reproductive system Muscle and bones
Why an organ or tissue is sensitive to a particular toxicants? The toxicants accumulates preferably in this organ/tissue Inactive pro-toxicants is activated in this organ/ tissue by phase I enzymes in high concentration The repairing system in the tissue is either less-developed or absent to the toxicant This tissue has receptors specific to this toxicant receptors on the cell membrane This tissue has an elevated physiological sensitivity to this toxicant
Variability of toxic response Individual-related (subjective) Living and working environmentrelated (objective)
Factors influencing the intensity of toxic response Age Gender Endocrine situation Nutritional habits Hereditary, previous disease & therapy Etc.
Types of toxic response Local Occurring only at the site of exposure of the organisms to the potentially toxic substance (skin, lungs, digestive tracts) Systemic Revealing itself after distribution of the toxicant via the bloodstream around the affected organism including the target organ or tissue, distinct from the absorption site.
According to the nature of their adverse effect on the target organs, the toxicants can be divided as: (1) Irritants Cause damage to the eyes & mucous membranes, ex: bromine, chlorine, ammonia, etc. Corrosive substances Corrode the skin & mucous membranes Substances that cause toxic pulmonary edema Chlorine, ammonia, nitrogen oxide Blockers of mitochondrial respiratory enzymes Cyanides, salicylic acid, gossypol
According to the nature of their adverse effect on the target organs, the toxicants can be divided as: (2) Inhibitors of thiol enzymes Heavy metals Blockers of Krebs cycle (citrate cycle) fluoroacetates Emetic substances Apromorphine, zinc, copper sulfate Neurotoxicants Cardiotoxicants Selectively damage the heart Ex: cardioglucosides, digitoxin, aconitine, etc.
According to the nature of their adverse effect on the target organs, the toxicants can be divided as: (3) Hepatotoxic substances Damage the liver Carbon tetrachloride, chloroform, etc. Nefrotoxic substances Damage the kidneys Mercury, chlorine, carbon tetrachloride, lead Substances that damage the bone marrow and blood cells Nirobenzene, etc.
According to the nature of their adverse effect on the target organs, the toxicants can be divided as: (4) Asphyxiants Substances that cause a reduction of blood’s ability to bind and transport oxygen Anticoagulants Substances that disturb blood coagulation Dicumarine, heparin, etc. Hemolytic substances Mushroom toxicants, phenyl-hydrazine, saponins, etc. Histamine and antihistaminic compounds
Based on the character of damage of a cell/ an organism, the toxic effects can be grouped as (1): Generally toxic Damage of the organism as a whole Dystrophic Causing the aging cells or tissues Genotoxic Alteration of the genetic material (DNA, RNA) Mutagenic Generation of irreversible changes in the hereditary materials (chromosomes, genes) of an organism
Based on the character of damage of a cell/ an organism, the toxic effects can be grouped as (2): Carcinogenic Genaration of malignant tumors Gonadotropic Harming and inhibiting the development of the germ cells Teratogenic Evoking disorders in the embryonal development of an organism Sensibilizating Making an organism ultrasensitive to this compound, resulting in allergic reactions and diseases
According to the final result, toxic responses can be grouped as: Direct injury of cell or tissue Biochemical damage Neurotoxicity Immunotoxicity Teratogenicity Genetic toxicity Carcinogenicity Endocrine disruption
Direct injury of cell or tissue Decomposition of cells (necrosis) An irreversible process consisting of degeneration of the cell, fragmentation of the nucleus, and denaturation of the cellular proteins. The cell disperses, accumulates liquid and its content flows out.
Direct injury of cell or tissue Mechanism: The formation of an intermediate that reacts with definite cell components like structural proteins. Examples: CN- ion or Pb can interact with the respiratory system of a cell --- leads to the death of a cell Strong alkalis or acids Strong oxidizers: ozone (O 3), Cl 2, Br 2, F 2 are very harmful to human and microorganisms.
Direct injury of cell or tissue Apoptosis – the programmed cell death Normal process for tissue renewal but it can be evoked by certain substances Example: trans-resveratrol (in grape wines) and its relatives (glucosides, etc).
Biochemical damage Biochemical injury cause: Degeneration of a single cell Influencing vital function of metabolism such as respiration The death of organism: Disruption of cell metabolism Deficiency of several organs
Neurotoxicity Compounds that have a toxic effect on the nervous system: Toxicants of the central nervous system (CNS) Toxicants of the peripheral nervous system (PNS) Toxicants of a combined effect
Neurotoxicity Many toxic compounds can cause serious brain impairment. Based on the mechanism of their effect, toxicants that have undesirable effect to the brain can be grouped: Neurotoxic compounds: These compounds can disturb the function of nervous system Mercury, acrylamide, hexane, CO 2, methyl-n-butylketone.
Neurotoxicity CNS inhibitor: Chlorinated hydrocarbons, benzene, aceton, dietyl eter Psychomimetics: They can disturb psychical activities Mescalin, phenylethylamine derivatives, indole derivaties Compounds that inhibiting the respiration center Narcotics, hydrocarbons
Neurotoxicity Convulsion toxicants Convulsion in central origin Organophosphorus pesticide Toxicants, paralyzing transmission of nerve impulses to the muscle Botulinin Toxicants, paralyzing transmission of nerve impulses in the nerve Tetrodotoxin
Neurotoxicity Neuroparalytic poisons: anticholinesteratic Toxicants, acting with mediators or synaptic poisons: Adrenaline, ephedrine, hydrazines, etc.