Mechanisms of Toxicity

What are 2 causes of toxicity? What are the 2 ADME mediated toxicity causes? ADME mediated and PD-mediated Peturbation - Perturbation of ADME leads to poor metabolization and higher chemical concentrations in the body. Metabolism - The metabolization of a non-toxic chemical leads to the generation of a toxic chemical. Disruption - The chemical disrupts the physiology of the cell via nonspecific pathways (e.g. oxidative stress, apoptosis, What are the 2 PD-mediated causes of necrosis, etc). toxicity? Interaction - The chemical interact specifically with biological targets, leading to specific target-mediated toxicity Drugs/chemicals can disrupt ADME processes What is ADME-mediated toxicity? This can change the pharmacokinetic profile of drug Reduced metabolization of a drug can result in higher-then-usual concentrations, increasing the risk of toxicological ADME-mediated toxicity: Effect on me- effects tabolism: Increased metabolization can result in lower than expected drug levels and reduced therapeutic effect They are drugs which lower the amount of 'bad' cholestrol in blood. What are statins? Lower the level of low-density lipoprotein (LDL) cholesterol in the blood CYP3A4 is a major cytochrome P450. 1/9 What are CYP3A4 Inhibitors? Potent inhibitors of CYP3A4 include clarithromycin, erythromycin What is Rhabdomyolysis? serious syndrome due to a direct or indirect muscle injury. It results from the death of muscle fibres and release of their contents into the bloodstream. This can lead to serious complications such as renal failure. What can Inhibitors of CYP34A do? Inhibitors of CYP34A can increase the serum concentrations of the active forms of these statins: Fibrates (especially gemfibrozil) Azole antifungal agents, Macrolides (especially erythromycin and clarithromycin, but not azithromycin) Protease inhibitors Calcium-channel blockers (especially verapamil and diltiazem) What is Clopidogrel? antiplatelet medication used to reduce the risk of heart disease and stroke in those at high risk and is activated in 2 steps proton pump inhibitor What is Omeprazole? used in the treatment of gastroesophageal reflux disease, peptic ulcer disease, to prevent upper gastrointestinal bleeding - traditional medicine - treat depressive and anxious states, nervousness, restlessness and sleep disorders What is St John's Wort? Clinical efficacy of St John's wort extracts at a daily dose of 500- 1800mg has been shown in mild to moderate depressive disorders (Marcus Mannel, 2012) 2/9 St John's Wort significantly induces intestinal and hepatic CYP3A4 What does st johns wort activate? To a lesser extent St John's Wort activates CYP2C19 and CYP2E1 Two drugs may compete for the same albumin binding site ADME-mediated toxicity: disruption of distribution: • According to their affinity to the binding site, one drug may displace the other causing an increase in the free concentration of the displaced drug. • This increase in free concentration may increase the risk of developing adverse effects, as it results in an increase of drug concentration at the target site. ADME-mediated toxicity: disruption of distribution example: • The administration of aspirin to a patient treated chronically with warfarin results in displacement of the latter from its binding site • the increase in plasma concentration of free warfarin causes serious haemorrhagic reactions. What is bioactivation (cause 2) ? The metabolic transformation of the chemical leads to a novel chemical species that is toxic. This process is known as bioactivation. What are the most important metabolic CYP450 and peroxidase enzymes, prosystems involved in bioactivation reac- ducing either electrophilic or radical tions? metabolites. What is a electrophilic metabolite? An electrophilic metabolite is a reactive, electron-deficient chemical compound formed during metabolic processes that can covalently bind to cellular biomolecules, potentially causing cellular damage or toxicity. 3/9 What is a radical metabolite? A radical metabolite is a highly reactive and unstable chemical species with unpaired electrons, known as a free radical, generated during metabolic processes, which can contribute to oxidative stress and cellular damage by initiating chain reactions with other molecules. What charge are electrophiles? They are typically either positively charged or have a partial positive charge (´+). If not detoxified properly, electrophiles can react with electron-rich species, i.e. nucleophiles (molecules containing negative centres), through covalent bond formation. What happens if electrophiles are not detoxified properly? resulting in the formation of adducts or conjugates. This covalent modification of biomolecules, such as proteins or DNA, can lead to cellular damage, dysfunction, and, in some cases, contribute to the development of diseases, including cancer. Electrophiles act as acceptors of electrons in a reaction What do electrophiles act as? What is a free radical? By accepting some electrons from nucleophiles, electrophiles will "quench" their positive or partial positive charge making a more overall stable species A molecule that is unstable and highly reactive because it contains unpaired electrons - react with another free radical to form a What do free radicals do rather than co- covalent bond valently bond with nucelophiles? - take a hydrogen atom from a neutral molecule to generate a new radical 4/9 - take an electron to form an anion and generate a radical cation What is an anion? A negatively charged ion What is a cation? A positively charged ion If not detoxified, reactive metabolites can cause the modification of biologiWhat happens if reactive metabolites are cal macromolecules resulting in cellular not detoxified properly? damage, dysfunction, and potential toxicity Example of reactive metabolites. One of the most frequently generated reactive intermediates What are Quinones? What can quinones form? can cause different toxicological effects in vivo including acute cytotoxicity, immunotoxicity, genotoxicity and carcinogenesis. Quinones are highly redox active molecules, leading to formation of ROS including superoxide, hydrogen peroxide, and ultimately the hydroxyl radical. Production of ROS can cause severe oxidative stress within cells through the forWhat can the production of ROS cause? mation of oxidized cellular macromolecules, including lipids, proteins, and DNA What is Remoxipride? Remoxipride is an atypical antipsychotic which was previously used in Europe for the treatment of schizophrenia and acute mania but was withdrawn due to toxicity concerns. What did paracetamol produce? Produces quinones It is estimated that between 82,000 and 90,000 patients present in the UK each year with paracetamol overdose. Between 150 and 250 deaths occur an5/9 nually in the UK, the vast majority in paHow many people overdose on parac- tients who have presented late, after a etamol? staggered overdose or after unintentional therapeutic excess. What can paracetemol do in high doses? Paracetamol can trigger severe liver toxicity in human patients at high doses What is meant by conjugation? Conjugation is an important mechanism for the rapid inactivation and extensive removal of drugs and poisons from the body, and as such it is of major significance in clinical toxicology. How is paracetamol conjugated? The major portion of paracetamol is conjugated with either sulfate or glucuronic acid to form water-soluble metabolites and only small amounts of the reactive intermediate: N-acetyl-pbenzoquinonimine (NAPQI) When therapeutic doses of paracetamol are ingested, the reactive intermediate What happens when a therapeutic does forms is efficiently deactivated by conof paracetamol is taken? jugation with the antioxidant glutathione (GSH). What happens when a large does of paracetemol is taken? When large doses are ingested the sulfate and glucuronide cofactors (PAPS and UDPGA) become depleted, resulting in more of the paracetamol being metabolized to the reactive intermediate. As long as GSH is available, most of the reactive intermediate can be detoxified. Why is GHS important in the liver? When the concentration of GSH in the liver also becomes depleted, NAPQI covalently bind to sulfhydryl (- SH) groups of various cellular proteins increases, resulting in hepatic necrosis. 6/9 If sufficiently large amounts of paracetaWhat happens with paracetamol over- mol are ingested, as in drug overdosdose? es and suicide attempts, extensive liver damage and death may result. Chemicals can induce non-specific toxic responses (i.e. not mediated by specific drug-target interactions) Examples: What are Non-specific toxic responses - Oxidative stress (cause 3) ? - Activation of cellular stress responses - DNA damage - Apoptosis - Necrosis - Immune or allergic response How is ROS generated? ROS are generated during the normal metabolism of oxygen via diverse enzymatic pathways. What is the main source of ROS? One of the main sources of ROS is the mitochondria, where the superoxide radical •O2 is produced as a by-product of normal oxidative phosphorylation. Drugs can induce oxidative stress by generating reactive oxygen species (ROS) during their metabolism.ROS, including free radicals, can cause cellular How can drugs induce oxidative stress? damage by oxidizing biomolecules such as lipids, proteins, and DNA, leading to disruptions in cell function, inflammation, and potential long-term harm. When mitochondrial DNA is the target of oxidation, it can lead to mutations, reWhat happens when mitochondrial DNA arrangements, and transcriptional errors that impair important mitochondrial comis target for oxidative stress? ponents, leading to more oxidative stress and eventual cell death. Cellular targets of ROS: DNA damage 7/9 What can oxidation of DNA lead to? oxidized bases (purines and pyrimidines) abasic sites (also called apurinic/apyrimidinic (AP) sites) DNA single- and/or double-strand breaks Guanine is the most susceptible DNA What is the most susceptible DNA base? base because of its low oxidation potential What is are the consequences of DNA Mutagenesis/Carcinogenesis/Teratogendamage? esis What is a mutagen? an agent, such as radiation or a chemical substance, that causes genetic mutation. What is carcinogen? cancer causing agent What is a teratogen? an agent or factor that causes malformation of an embryo. Drug hypersensitivity reactions (DHR) include allergic, exaggerate, pharmacologWhat do drug hypersensitivity reaction ic, and pseudo-allergic reactions to medinclude? ications that result from an enhanced immunologic or inflammatory response. What is Target-mediated toxicity (cause 4) ? It's when chemicals can interact with specific biological targets (e.g. receptors, enzymes, ion channels). These interactions cause alteration of normal biological pathways leading to the disruption of the system. Pharmaceuticals companies use a range of computational and in vitro assays to Target-mediated toxicity: drug developpredict whether a new drug can interact ment: with targets that are known to be associated with serious adverse effects. What is hERG? an example of a safety target 8/9 What does hERG do? hERG (the human Ether-à-go-go-Related Gene) is a gene (KCNH2) that codes for a protein known as Kv11.1, the alpha subunit of a potassium ion channel. This ion channel is essential to regulate the electrical activity of the heart. The hERG channel mediates the repolarizing IKr current in the cardiac acWhat does the hERG channel mediate? tion potential, which helps coordinate the heart's beating hERG inhibition can result in a potentially fatal disorder called long QT syndrome What can hERG inhibition cause? What is long QT syndrome? A number of drugs have the tendency to inhibit hERG, lengthening the QT and potentially leading to a fatal irregularity of the heartbeat Long QT syndrome (LQTS) is a heart rhythm disorder that can potentially cause fast, chaotic heartbeats. These rapid heartbeats may trigger a sudden fainting spell or seizure. In some cases, your heart may beat erratically for so long that it can cause sudden death. 9/9