Cellular toxicology Flashcards
What is included in cytotoxic agents?
Cytotoxic agents include toxic metals, chemicals, radiation, drugs and nanomedicines
What is oxidative stress?
Caused by an excessive quantity of free radicals and reactive oxidants (ROS), which are formed from oxygen/water/hydrogen peroxide. They are naturally produced as a by product of metabolism in mitochondria, but can also be induced by exogenous sources such as toxins.
The generation of reactive oxygen species (ROS) leading to oxidative stress causes damage to cellular components (DNA, proteins, lipids)
How does mitochondrial dysfunction lead to cellular toxicity?
Interreference with mitochondria leads to impaired energy function and increased ROS generation.
Accumulation of nanoparticles can lead to mitochondrial damage, leading to;
excessive ROS production (see oxidative damage), and
the release of cytochrome C from the mitochondria that signal apoptosis to the cell
How does the immune system activation cause cytotoxicity?
Immune response can be activated in response to the foreign nanoparticles, can lead to hypersensitivity
Inflammation – activating immune cells can trigger the release of pro-inflammatory cytokines causing tissue damage and chronic inflammation
How does DNA or membrane damage lead to cytotoxicity?
DNA damage – interaction with DNA can cause mutations and strand breaks. Can lead to genomic instability and contribute to carcinogenesis
Membrane damage – disrupting cell membranes leads to loss of membrane integrity and cell lysis
What is protein corona formation?
Nanoparticles can absorb proteins onto their surface forming protein corona, altering the nanoparticle properties and interactions
What is apoptosis?
A controlled and energy-dependent process.
Cellular changes – apoptotic cells undergo cell shrinkage, chromatin condensation, DNA fragmentation and membrane blebbing. This makes it easier for phagocytes to engulf.
Formation of apoptotic bodies – cell breaks down into small, membrane-bound fragments (apoptotic bodies) which are engulfed and removed by phagocytes preventing inflammation.
What is the intrinsic/mitochondrial pathway to apoptosis?
Triggered by internal signals (DNA damage, oxidative stress etc.) leading to release of proteins like cytochrome C from mitochondria, and the activation of caspases (proteases, cleave specific proteins to be engulfed by phagocytes)
Can lead to swelling of mitochondria, leading to opening of pores on the mitochondria. This releases cytochrome C, which binds to ATP, APAF-1 and Procaspase-9 to create a protein complex known as an apoptosome.
The apoptosome cleaves procaspase-9 to its active form, which then cleaves the executor caspase-3/7 and activates it
What is the extrinsic pathway to apoptosis?
Triggered by external signals (binding of death ligands) which leads to formation of death-induced signaling complex (DISC) and the activation of caspases
Receptor activation leads to recruitment of TNF-receptor-associated death domain (TRADD) and FAS-associated death domain (FADD). This causes the formation of DISC which includes procaspase-8
Caspase-8 is cleaved and activated, then activated executor caspase-3/7
What is necrosis?
Unregulated rapid cell death due to loss of membrane integrity
Leads to inflammation and damage to surrounding tissues.
Caused by infections, trauma, toxins, or ischemia (reduced blood flow).
The cell swells, ATP is depleted, DNA fragmentation is random or smeared, the whole areas of tissue are affected.
What are some common reactive oxidants or free radicals?
Common reactive oxidants - ozone (O3), singlet oxygen (1O2), hypochlorous acid (HOCl), nitrous acid (HNO2), peroxynitrite (ONOO–), dinitrogen trioxide (N2O3) and lipid peroxide (LOOH)
Free radicals have unpaired electrons. They can react with DNA, proteins and lipids causing damage and leading to cell stress (and cell death)
Common free radicals – hydroxyl (OH), superoxide (O2-), nitric oxide (NO), nitrogen dioxide (NO2), neroxyl (ROO) and lipid peroxyl (LOO)
What are some examples of antioxidants?
ROS are kept in check by antioxidants, including antioxidant enzymes;
Superoxide dismutase (DOS) - superoxide radicals converted into oxygen and hydrogen peroxide
Catalase (CAT) - hydrogen peroxide converted into water and oxygen
Glutathione peroxidase (GPx) - lipid hydroperoxides converted into alcohol, and free hydrogen peroxide converted to water
Other antioxidants include vitamin C, vitamin E, selenium, flavonoids etc.
What are the 2 types of inflammation?
Acute inflammation – protective as it removes damaged cells and tissues from the body
Prolonged/chronic inflammation – often destructive as it can lead to tissue damage and contributes to development of cancer, cardiovascular disease and neurodegenerative disorders
Explain the pathway of inflammation
Inducers – chemicals, nanoparticles, toxins etc. lead to tissue damage
Tissue damage leads to the release of DAMPs/PAMPs and TNF/ILs which are recognized by immune cell receptors
Sensors – Immune cells (mast cells, dendritic cells and macrophages) produce mediators including cytokines, TNF, histamine, bradykinin and eicosanoids
Target tissue – mediators induce vasodilation, extravasation (WBCs move out of bloodstream into tissue) of neutrophils and leakage of plasma into infected/damaged tissue
What are the signs of inflammation?
Heat – blood vessels dilate to allow more blood to reach site of infection/injury
Redness – dilation of blood vessels and increased blood flow to area
Swelling – accumulation of fluid due to increased permeability of blood vessels from inflammatory mediators, allowing immune cells and proteins to leak into tissue
Pain/tenderness - prostaglandins and bradykinin released sensitize nerve endings
loss of function – swelling and pain can limit movement and function
What are PAMPs and DAMPs?
Pattern recognition receptors (PRRs) are found on immune cells and recognize molecules associated with pathogens (PAMPs) and tissue damage (DAMPs)
DAMPs -
Endogenous danger signals that are discharged to extracellular space in response to damage or stress.
Include heat shock proteins, mitochondrial DNA and histones.
DAMP promote a sterile inflammatory response by binding to PRRs on immune cells.
Sterile molecules such as nanomedicines can potentially be antigenic and induce an immune response, through recognition by antibodies on B cells. Nanoparticles can be processed and presented on the surface of cells by MHC to be recognised by T-cells.
What are some examples of organic nanoparticles?
Polymeric nanoparticles (e.g. nanosphere, nanocapsule, micelle) - used in drug delivery and tissue engineering. Can cause oxidative stress and inflammation depending on polymer type
Liposome – used in drug delivery (enhances bioavailability). Can cause immune reactions and complement activation in some cases
Dendrimer
Fullerenes – used in drug delivery and antioxidants. Can cause oxidative stress and cytotoxicity depending on functionalization
What are some examples of inorganic nanoparticles?
Mesoporous silica nanoparticle – used in drug delivery and imaging agents. Can cause oxidative stress, inflammation and lung toxicity
Carbon nanotube – used in drug delivery (biosensors). Can cause inflammation, pulmonary toxicity and fibrosis when inhaled
Iron oxide nanoparticle – used in MRI and drug carriers. Can cause oxidative stress, inflammation and neurotoxicity
Gold nanoparticle – used in drug delivery and imaging. Can induce oxidative stress and inflammation
Silver nanoparticle – used in wound dressings and coatings. Can cause mitochondrial dysfunction, oxidative stress and DNA damage
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