Toxicology Exam 1 Flashcards
Toxicology
the study of the adverse effects of substances on living organisms
- Chemical properties
- Biological effects
- Concentration/dosage, duration, and frequency of exposure
Toxicant
any chemical that interferes with life, biological processes, and exert a deleterious effect on an organism
Toxin
poison originating from a biological process (an organism)
Biotoxin
synonymous with toxin
Bacterial toxin
toxin originating from a bacterium; an endotoxin or exotoxin
Zootoxin (venom)
toxin originating from an animal
Phytotoxin
toxin originating from a plant
Toxicosis
the disease or illness that results from exposure to a poison
Intoxication
the state produced by exposure to a poison
What are the 4 classifications of toxicity exposures?
Acute
Subacute
Subchronic
Chronic
Acute toxicity
> /= 1 exposure within a 24 hour period
Subacute toxicity
> 1 exposure for 1-30 days
Subchronic toxicity
n exposures for 1-3 months
Chronic toxicity
n exposures for >3 months
What are toxic effects?
the adverse effects produced in an organism when it is exposed to a poison
* Death
* Sickness
* Disease
Teratogenic effects
Malformations in a fetus that result from exposure to chemicals in utero
Mutagenetic effects
genetic mutations caused by exposure to chemicals
Carcinogenic effects
cancer caused by exposure of chemicals
What is the difference of pharmacology vs toxicology?
Both pharmacology and toxicology are scientific principles that focus on understanding the properties and actions of chemicals. However, pharmacology emphasizes the therapeutic effects of chemicals, usually drugs or compounds that could become drugs. Whereas toxicology is the study of chemical’s adverse effects and risk assessment
Exposure (unintended) vs Dosage (intended)
Adverse drug reactions
Absorption of toxicants meaning
transport across membrane
- Absorption determines toxicity of chemicals
- Absorption of toxicants require movement across one or more membranes
What are the four types of transports/absorptions of toxins?
Passive, Active, Facilitated and Endocytosis
Passive transport
= diffusion
* Movement is down concentration gradient
* Does not require energy. Most common means of absorption
* Hydrophobic, uncharged molecules
Active transport
- Required a “pump of energy”
- Pumps against concentration gradient
- Different pumps for different chemicals
- Saturable (maximal pumping speed)
- May be inhibited (stops pumping)
Facilitated diffusion
- Required a channel or pore
- Requires NO energy
- May become saturated (maximal transport speed)
- May be inhibited (stops transporting)
- Moves chemicals DOWN concentration gradient
Endocytosis
- Large molecules and particles
- In endocytosis, the cell surrounds the “cargo” with its cell wall. The engulfed cargo separates from the membrane and moves into the interior of the cell
The two main forms of endocytosis are:
Phagocytosis (cell-eating) – large particles are engulfed and either transported and/or destroyed within the cell.
Pinocytosis (cell-drinking) – similar, but involves the engulfing of liquids or very small particles
Factors influencing SIMPLE DIFFUSION
- Ionization
- Diffusion (Fick’s law)
- Permeability / partition coefficients
How does ionization influence simple diffusion?
unionized (has not formed an ion) forms of drugs and toxicants can pass through membranes more readily than ionized formed; Henderson-Hasselbach equation
How does diffusion (Fick’s law) influence simple diffusion?
rate of diffusion depends upon concentration gradient, absorptive area, and thickness of membrane
How does permeability / partition coefficients influence simple diffusion?
Depends on partitioning, mobility, and thickness of the membrane
Partition coefficients – ratio of solubility in hydrophobic (organic) vs hydrophilic (water solvent). Membranes are more permeable to chemicals with high partition coefficients
Routes of absorption
Gastrointestinal, respiratory. skin, mucosa
Gastrointestinal (oral) route of absorption
very common route for toxicants in food and water
Respiratory system route of absorption
gaseous or vaporous toxicants, some particulates; highly influenced by circulation
Skin route of absorption
relatively impermeable, but some chemicals absorbed across it; injury, hair follicles, sebaceous glands, penetration; lipophilic chemicals penetrate more readily
Mucosa route of absorption
high degree of absorption
Xenobiotic metabolism (Biotransformation): Good and bad effects
- Alter solubility (hydrophilicity) or enhance exertion (detoxification)
- Increase toxicity
Phase I reactions
- Degradation (catabolic) reactions
Biotransformation occurs primarily in the ER and cytosol and to a lesser extend in the mitochondria, nuclei, and lysosomes. Functional group can be added.
Phase II conjugation reactions
- Conjugation reactions (anabolic)
o Except for glucuronide formation, most occur in the cytoplasm
What are the different types of phase I reactions?
- Oxidation: loses electrons
- Reduction: gains electrons
- Hydrolysis: adds water
What are the types of phase II conjugation reactions?
Glucuronide formation
Sulfate formation
Methylation
Acetylation
Amino acid conjugation
Glutathione conjugation
Glucuronide formation
Modification, enzyme, and co-factor
– addition of glucoronate, very common mechanism.
Catalyzed by UDP-glucuronly transferase in endoplasmic reticulum
coenzyme = UDPGA
Sulfate formation
Modification, enzyme, and co-factor
– addition of a sulfate.
Catalyzed by sulfotransferase in cytosol
coenzyme = PAPS.
Methylation
Modification, enzyme, and co-factor
Addition of methyl.
Catalyzed by methyl transferase
coenzyme = SAM
Acetylation
Modification, enzyme, and co-factor
Addition of acetyl group.
Catalyzed by N-acetyl transferases
coenzyme = acetyl CoA
Amino acid conjugation
Modification
– addition of amino acids
Glutathione conjugation
Modification, enzyme, and co-factor
Binding to glutathione GSH
Catalyzed by glutathione S-transferases
cofactor = glutathione
Bioactivation
chemically stable compound converted to chemically reactive metabolite. Often catalyzed by cP450 enzymes
- Reactive metabolite binds to macromolecules (proteins, nucleic acids) causing cell damage (death)
Example of metabolism and consequence
Epoxide formation – aromatic compounds converted to epoxide.
–> epoxide is conjugated with GSH; conjugated product is not toxic.
If capacity for conjugation is exceeded, epoxide becomes available to damage tissues (hepatocellular carcinoma).
Routes of excretion
Primary routes of excretion:
1. Urinary
2. Fecal/biliary
3. Respiratory
Secondary routes of excretion:
1. Sweat
2. Tears
3. Saliva
4. Milk
Toxidynamics
the dynamic interactions of a toxicant with a biological target or site of action, and its biological effects (dose-response)
Threshold concentration
concentration above which toxic effects occur.
Toxicokinetics
how a toxicant gets into the body and what happens to it within the body (concentration-time course relationship)
- Movement of toxicant in the body
o Terminal half-life
o Volume of distribution.
LOEL
lowest observed effect level. Lowest dose at which an effect (even beneficial) is observed
LOAEL
lowest observed adverse (judgmental) effect level. Lowest dose at which an adverse effect was detected.
NOEL
no observed effects level. Highest dose (tested) at which a significant effect (even beneficial) could not be found
NOAEL
no observed adverse effects level. Highest dose (tested) at which a significant adverse effect could not be found.
LD50
lethal dose 50%. Statistically derived dose at which 50% of animals will be expected to die
Steps of toxicity after xenobiotic exposure
Step 1: Toxicant delivery
Step 2: Reaction of the toxicant (metabolite) at the site of action
Step 3: Toxicant-induced cellular dysfunction or injury
Step 4: Adaptation of Repair
Toxicant delivery after xenobiotic exposure
- The intensity and nature of the toxic effect depends on the concentration and length of toxicant (metabolite) exposure
- The concentration of the toxicant (metabolite) at the site of action depends on the balance between the processes that increase and decrease its concentration
Reaction of the toxicant (metabolite) at the site of action after xenobiotic exposure
- Depends on attributes of the target molecule, types of reactions, and effects/outcomes
Toxicant-induced cellular dysfunction or injury after xenobiotic exposure
- At the cell/organ/tissue/system level
- Dysfunction involved all aspects of cell physiology
o Growth/proliferation
o Differentiation
o Function
o Survival
Adaptation or repair after xenobiotic exposure
- Cells and tissues will adapt first, succumb second
- Repair mechanisms for biomolecules and organelles
- Degradation and turnover
- Transcriptional regulation of adaptive mechanisms
- Tissue responses
Redox signal transduction
signaling process that involved redox reactions
Types of reactions mediated by toxicant
Non-covalent
Covalent
Hydrogen abstraction
Electron transfer
Non-covalent reaction mediated by toxicant
Reversible hydrogen / ionic bonds (ion channels and membrane receptors)
Covalent reaction mediated by toxicant
Irreversible adduct formation by electrophiles (–> nucleophiles)
Covalent reaction mediated by toxicant
Irreversible adduct formation by electrophiles (–> nucleophiles)
Covalent reaction mediated by toxicant
Irreversible adduct formation by electrophiles (–> nucleophiles)
Covalent reaction mediated by toxicant
Irreversible adduct formation by electrophiles (–> nucleophiles)
Covalent reaction mediated by toxicant
Irreversible adduct formation by electrophiles (–> nucleophiles)
Hydrogen abstraction reaction mediated by toxicant
- Free radicals to generate more radicals
- Protein carbonyls (DNA or protein adducts)
Electron transfer reaction mediated by toxicant
Oxidation or reduction of molecule
Covalent reactions by Electrophiles
- Covalent binding forms irreversible bonds between a toxicant and the target molecule
- Between electrophilic (electron-seeking) toxicants and nucleophilic (electron-donating) compounds.
- Nucleophilic compounds are abundant in biological systems (proteins, nucleic acids, and phospholipids)
- Covalent binding of toxicants can inhibit or alter enzymes, protein function, or damage cellular components.
Oxidation
–> is the loss of electrons or an increase in the oxidation state of an atom
o Compounds that easily take up electrons can often oxidize other molecules – oxidants
Reduction
–> is the gain of electrons or a decrease in the oxidation state of an atom
o Compounds that easily donate electrons have a tendency to reduce other molecules – reductants
Redox Cycling
Repetitively coupled reduction and oxidation reactions, often involving oxygen and reactive oxygen species (ROS)
Oxidative stress
an increase in the steady state levels of ROS (or derived oxidative modifications) that surpasses the ability of the cell to counteract them (oxidant systems, repair/ turnover mechanisms). Imbalance between ROS generation and antioxidant systems
Reactive oxygen species
A type of unstable molecule that contains oxygen and that easily reacts with other molecules in a cell. A build up of reactive oxygen species in cells may cause damage to DNA, RNA, and proteins, and may cause cell death. Reactive oxygen species are free radicals.
Reactive nitrogen species
Reactive oxygen species/reactive nitrogen species derived from oxygen and nitrogen plays a vital role in propagation of liver injury by damaging cell membrane, micro, and macromolecules. Excess ROS production leads to various diseases especially liver which have its main function as detoxification.
ROS or RNS
are chemically reactive molecules containing oxygen
o RNS are considered a subtype of ROS as they contain oxygen
- ROS / RNS are by products of metabolism or ROS-generating enzymes activated during inflammation
Polyunsaturated acyl chains of phospholipids or polyunsaturated fatty acids (PUFAs) such as arachidonic acid and linoleic acid are highly susceptible to peroxidation and breakdown forming a variety of lipid-derived aldehydes and ketones
o When lipid encounters a free radical, will split and become a lipid radical
o Compounds are not stable, fragment from membrane and produce aldehydes (which are toxic)
Inflammation
is a reaction to injurious agents (microbes, damaged cells, or xenobiotics) that leads to the systemic responses mediated by the release of cytokines
- Transcriptional regulation of gene expression
Inflammation is a protective response, the ultimate goal of which is to clear the organism of both the initial cause of cell injury and the consequences of such injury
- Acute inflammation
is the initial response of the body to harmful stimuli and is achieved by the increased movement of plasma and leukocytes from the blood into the injured tissues
Chronic inflammation
is characterized by simultaneous destruction and healing of the tissue from the inflammatory process.
Inflammation- Induced Oxidative Damage
Oxidative stress can cause chronic inflammation. Infections and injuries trigger the body’s immune response. Immune cells called macrophages produce free radicals while fighting off invading germs. These free radicals can damage healthy cells, leading to inflammation.
NADPH Oxidases (NOx’s)
are transmembrane proteins responsible for transporting electrons across biological membranes, which leads to reduction of oxygen into superoxide
o Oxidative burst in response to pathogens
Nitric oxide synthases (NOSs)
Are a family of enzymes catalyzing the production of nitric oxide (NO) from L-arginine. NO is an important cellular signaling molecule
What are the cell death pathways
Apoptosis
Necrosis
Autophagy
Apoptosis
Programmed cell death. Apoptosis is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, DNA fragmentation, and mRNA decay.
o clearance by phagocytic cells
Necrosis
Accidental; release of the intracellular content. Irreversible and accidental cell injury. Loss of plasma membrane integrity, cell/organelle swelling, robust inflammatory response
Autophagy
Uncontrolled or when targeting vital organelles; mostly a protective mechanism. Homeostatic mechanisms are involved in the turnover or degradation of cellular components of pathogens.
o Cargo is engulfed in double-membraned autophagosomes to be later degraded upon fusion with lysosomes
o Involved activation of a # of signaling platforms: initiation, elongation, maturation, fusion, recycling
What determines how a cell dies?
- Intensity and length of toxic stimuli
- Signaling pathways activated
- Integrity and functionality of signaling machinery (apoptosis)
- Mitochondria injury
How do xenobiotics induce anemia?
Xenobiotics affect the production, function, or survival of erythrocytes resulting in decrease cell mass (anemia).
Erythrocytes and heme–> principle transport vehicle for O2 transportation from the lung to peripheral tissues, and CO2 from tissues to the lung.
Proliferation (Erythropoietin)
EPO tells your body to make red blood cells. When you have kidney disease, your kidneys cannot make enough EPO. Low EPO levels cause your red blood cell count to drop and anemia to develop.
Xenobiotic effects on proliferation
Toxicants can affect the supply of nutrients (iron) or growth factors (erythropoietin). Erythropoietin (EPO) is a glycoprotein hormone, naturally produced by the peritubular cells of the kidney, that stimulates red blood cell production.
Heme formation
Erythrocyte production depends on cell division and high rates of heme production.
Pb (Lead) effect on anemia
Inhibits the ability to produce hemoglobin by interfering with enzymatic steps in the heme synthesis pathway and diminishes red blood cells, thereby increasing risk of anemia. The absorption of lead can cause iron deficiency and may further cause anemia
Defects in the synthesis of the porphyrin ring of heme lead to sideroblastic anemia. Accumulation of iron in bone marrow.
Enzymes of Pb (lead) effecting anemia
Defects in the synthesis of the porphyrin ring of heme lead to sideroblastic anemia. Accumulation of iron in bone marrow.
Enzymes of Pb (lead) effecting anemia
Defects in the synthesis of the porphyrin ring of heme lead to sideroblastic anemia. Accumulation of iron in bone marrow.
- Porphobilinogen synthase (or ALA dehydratase or aminolevulinate dehydratase) synthesizes porphobilinogen from aminolaevulinic acid.
- Ferrochelatase catalyzes the insertion of iron into protoporphyrin IX.
Ferrochelatase and ALA dehydratase are inhibited by lead.
How does carbon monoxide impair O2 delivery?
Carbon monoxide (CO) – an odorless, colorless gas. Causes sudden illness and dead by impairing O2 binding to hemoglobin.
When carbon monoxide binds to hemoglobin, less oxygen gets transported to body tissues and vital organs such as the brain and heart. The bond between carbon monoxide and hemoglobin is approximately 250 times stronger than the bond between oxygen and hemoglobin.
How do xenobiotics trigger leukemogenesis?
Proliferative disorders of hematopoietic tissue that originate from bone marrow and cells
Myeloid leukemogenesis
(myeloblasts, RBCs, and platelets) or lymphoid (lymphocytes)
Acute leukemogenesis
(poorly differentiated) or chronic (well differentiated)
Main difference between myloid and acute leukemogenesis
Myeloid affects the production of myeloblasts, red blood cells, and platelets, whereas Acute mainly affects the production of lymphocytes
Examples of how xenobiotics trigger leukemogenesis
o Ionizing radiation
o Chemicals
Benzene –> occupational exposure to benzene via inhalation is associated with acute myeloid leukemia. Travels to bone marrow where it can undergo different biosynthetic pathways.
Alkylating agents
Mechanisms involved in effects of Toxicants in the Immune System
Elimination or control: recognition, memory, response
Bone marrow (origin; NK cells), thymus (T cells; activated and memory), spleen and lymph nodes (B-cells; antigen presenting)
Three effects of toxicants on immune system:
- Immunosuppression and immunodeficiency
- Hypersensitivity and allergy
- Autoimmunity
Immunosuppression and immunodeficiency
increase risk to infections and diseases associated with it
Autoimmunity
antibodies to endogenous antigens. Mode of action of drugs or toxicants appears to be through covalent binding of the drug or its metabolites to tissue macromolecules,
Types of hypersensitivity reactions
Anaphylactic, cytolysis, immune complexes, and cell mediated (nickle)
Anaphylactic hypersensitivity reaction
antigens crosslink IgE and release vasoactive molecules
Cytolysis hypersensitivity reaction
antigen binds to IgM or IgG on the foreign/ host cell leading to its death
Immune complexes hypersensitivity reactions
soluble antigen-antibody immune complexes not cleared by immune cells leave the plasma and are deposited in tissues triggering an inflammatory reaction
Cell-mediated (nickel) hypersensitivity reaction
development of activated and memory T-cells
Vulnerable targets in cardiomyocyte function
Heart and blood vessels
How is the heart affected by xenobiotics
alteration of the electrophysiology of the heart resulting in the impairment of its mechanical function
o Most vulnerable mechanisms: energy
How are blood vessels affected by xenobiotics?
permeability, damage, atherosclerosis
Effect of xenobiotics on cardiac action potential
- Local anesthetics –> Na + channel blockage
- General anesthetics and antipsychotic drugs –> Ca 2+ channel blockages
- Antihistamines –> K+ channel blockers
Glycosides
Found in plants
o Inhibition of the Na+ / K+ ATPase
o Cardiac arrythmias or arrest, hemorrhage, myocarditis, and myocardial ridges
o Digitonin from Digitalis purpurea
Alkaloids
Found in plants
o Acetylcholinesterase inhibitors (regulation of HR via muscarinic Ach-receptors and K+ channels)
o Ca 2+ antagonists
Indexes of cardiotoxicity
- Changes in the electrocardiogram (ECG)
Increase in the amplitude of the T-wave and St-segment elevation - Serum levels of troponin T and I
- Levels of creatinine kinase CK, MB, FABP3, and Lactate Dehydrogenase LDH-1
Biomarkers for cardiac toxicity and where they act
Creatine kinase –> myocardium
Myoglobin –> myocardium
B-type natriuretic peptide BNP –> ventricular myocardium
Cardiac troponins –> cardiomyocytes
Key characteristics of cardiovascular toxicants:
- Impairs regulation of cardiac excitability
- Impairs cardiac contractility and relaxation
- Induces cardiomyocyte injury and death
- Altern hemostasis (bleeding prevention and stop)
- Impairs mitochondrial function
- Modifies autonomic nervous system activity
- Induces oxidative stress
- Causes inflammation
What is an endocrine disruptor?
Endocrine disruptors are chemicals that interfere with the hormone systems and produce adverse developmental, reproductive, neurological, and immunological effects in mammals.
- Present in the environment and foods
- Derives from different sources: pharmaceuticals, pesticides, plastics, byproducts of combustion metals
How do endocrine distrupters act?
- Mimic or interfere with the action of hormones
- Affect the synthesis, storage, and release of hormones
What can endocrine disruptive chemicals induce?
- Developmental toxicity
- Reproductive toxicology
- Neurotoxicity
- Immune toxicity
- Mutagenesis
- Obesity and diabetes
General signaling by nuclear hormone receptors
Nuclear receptor signaling (steroids) –> hormone is a ligand that needs to bind to a receptor
How does Nuclear receptor signaling work?
- Ligand-regulated transcription factors activated by hormones
- Their ligands cross the plasma membrane and interact with nuclear receptors inside the cell
- Once activated, nuclear receptors directly regulate transcription of genes that control a wide variety of biological processes
Epigenetics
alterations of genes that do not include alterations in the DNA sequence. Regulation of phenotypic trait variations (cellular or physiological) by external or environmental factors that switch genes on and off and affect how cells read genes without alterations in the DNA sequence.
What is the role of DNA methylation + histone modifications?
DNA methylation is essential for silencing retroviral elements, regulating tissue-specific gene expression, genomic imprinting, and X chromosome inactivation. Importantly, DNA methylation in different genomic regions may exert different influences on gene activities based on the underlying genetic sequence
DNA methyltransferases catalyze the transfer of a methyl group to DNA using SAM as the methyl donor
Obesogens
are foreign chemical compounds that are hypothesized to disrupt normal development and balance of lipid metabolism, which in some cases, can lead to obesity
Agents that act in a variety of ways to promote fat storage and adipose tissue production, often by disrupting hormonal signaling
Tributyltin –> peroxisome proliferator
Glucocorticoid receptor
What is the contribution of obesogenic xenobiotics to the epidemic of obesity?
Effects perpetuated through generations, presumably via epigenetic mechanisms
Mechanisms of toxicity by goitrogenic substances
Goitrogens are naturally occurring substances that can interfere with the function of the thyroid gland. Goitrogens get their name from the term ‘goiter’ which means the enlargement of the thyroid gland. This triggers the pituitary to release thyroid-stimulating hormone (TSH), which then promotes the growth of thyroid tissue, eventually leading to goiter.
Mechanisms of toxicity by goitrogenic substances
Goitrogens are naturally occurring substances that can interfere with the function of the thyroid gland. Goitrogens get their name from the term ‘goiter’ which means the enlargement of the thyroid gland. This triggers the pituitary to release thyroid-stimulating hormone (TSH), which then promotes the growth of thyroid tissue, eventually leading to goiter.
