1. Causes & Targets of Cell Injury
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Al-Quds University
Assistant professor of pathology.
Faculty of Medicine
Pathology Department

2. Cell injury: What are the causes?
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Cell injury: What are the causes?
Physical
Chemical
Infectious
Immunological
Nutritional
Genetic
Oxygen Deprivation
Aging

3. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Physical agents
Mechanical trauma
Thermal: heat or cold
Radiation
Electrical shock

4. Causes and Targets of Cell Injury
Chemical agents
Dr. Marwan Qubaja / Pathology I
Drugs & Poisons

5. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Infectious agents
Viruses, bacteria, fungi, parasites, tapeworms

6. Immunological reactions Antigen – antibody reactions
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Immunological reactions Antigen – antibody reactions
Major role in defence against infectious pathogens
If overridden or improperly operating it will result in diseases:
Anaphylactic reaction:
reaction to a foreign protein or a drug
2. Autoimmune diseases:
reactions to endogenous self-antigens

7. Immunological reactions Antigen – antibody reactions

8. Nutritional imbalance
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Nutritional imbalance
Undernutrition
Protein-calorie deficiencies
Vitamins & Mineral Deficiencies
Anorexia nervosa
Overnutrition
Atherosclerosis
Obesity

9. Causes and Targets of Cell Injury
Genetic Defects
Dr. Marwan Qubaja / Pathology I
Examples:
Down syndrome
Sickle cell anemia
Inborn errors of metabolism
Substitution of valine for glutamic acid at the sixth position of the β-globin chain produces sickle Hb (HbS).

10. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Oxygen deprivation
Hypoxia, or oxygen deficiency, interferes with aerobic oxidative respiration
Hypoxia = continue glycolysis
Ischemia, which is a loss of blood supply in a tissue due to impeded arterial flow or reduced venous drainage.
Ischemia nutrients
Ischemia is the most common cause of hypoxia
Ischemia is the most common type of cell injury O2 O2

11. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Oxygen deprivation
Ischemia
Anemia
high altitude
respiratory failure
blood supply CO
glucose
Hypoxia: blood oxygenation
oxygen deficiency can also result from inadequate oxygenation of the blood, as in pneumonia, or reduction in the oxygen-carrying capacity of the blood, as in anemia or carbon monoxide (CO) poisoning (CO forms a stable complex with hemoglobin that prevents oxygen binding).
Ischemia is more severe than hypoxia because it impairs the oxygen and substrate delivery as well as the removal of waste.
cell death

12. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Aging

13. Cellular aging: Mechanisms
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Cellular aging: Mechanisms
INTRINSIC
EXTRINSIC

14. Overview of Cell Injury
Causes and Targets of Cell Injury
Overview of Cell Injury
Dr. Marwan Qubaja / Pathology I
The cellular responses to injurious stimuli depend on the type, duration, and severity of injury.
The main targets for the injury are:
(1) cell membrane integrity
(2) ATP generation
(3) protein synthesis
(4) the integrity of the genetic apparatus

15. Cellular & biochemical mechanisms
Causes and Targets of Cell Injury
Cellular & biochemical mechanisms
Dr. Marwan Qubaja / Pathology I
Loss of membrane integrity
ATP depletion and mitochondrial damage
Increased intracellular calcium
Free radical-induced injury
Protein breakdown
DNA damage

16. Cellular & biochemical mechanisms
Causes and Targets of Cell Injury
Cellular & biochemical mechanisms
Dr. Marwan Qubaja / Pathology I
e.g. Ischemia

17. Loss of calcium homeostasis
Causes and Targets of Cell Injury
Loss of calcium homeostasis
Dr. Marwan Qubaja / Pathology I
Cytosolic is normally maintained by ATP-dependent transporters
Injury allows a net influx of extracellular across the plasma membrane, followed by the release of from the intracellular stores.
Cell injury results in increased intracellular cytosolic
Ca2+
Ca2+
Ca2+
Ca2+
Cytosolic free calcium is normally maintained by ATP-dependent calcium transporters at concentrations that are up to 10,000 times lower than the concentration of extracellular calcium or of sequestered intracellular mitochondrial and endoplasmic reticulum calcium. Ischemia or toxins allow a net influx of extracellular calcium across the plasma membrane, followed by the release of calcium from the intracellular stores. Increased cytosolic calcium in turn activates a variety of phospholipases (promoting membrane damage), proteases (catabolizing structural and membrane proteins), ATPases (accelerating ATP depletion), and endonucleases (fragmenting genetic material) (Fig. 1-4). Although cell injury results in increased intracellular calcium, and this in turn mediates a variety of deleterious effects, including cell death, a loss of calcium homeostasis is not always a necessary proximate event in irreversible cell injury.
Calcium is very important, since it acts as secondary messenger for the activation of different enzymes within the cell cytoplasm, like protein kinase, leading to loss of the integration of the cell.
Ca2+

18. Mitochondrial damage & ATP Depletion
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
ATP synthesis pathways:
mitochondrial oxidative phosphorylation
anaerobic glycolysis
ATP function:
the maintenance of cellular osmolarity
transport processes
protein and lipid synthesis
basic metabolic pathways
Inner
Membrane
Outer
Cristae
Matrix
Intermembrane
Space
DNA
Ribosome
Granule
0.1 -
0.5 m 1 2
The main function and the central role of mitochondria is production of energy inside the cell in the process of oxidative phosphorylation that supplies ATP for organs (Duchen, 2004). Mitochondria are the main source of energy that sustains cellular metabolism and integrity. In general, there are two pathways for energy production: the first is glycolysis, which involves the breakdown of glucose and ATP synthesis in a reaction that takes place in the cytosol. The second is oxidative phosphorylation through the mitochondria. The chemical energy released by mitochondrial oxidations is used to generate ATP, which is the major energy-carrying molecule of the cell. In major mammalian tissues, it is estimated that 80 to 90 % of ATP is generated by the mitochondria
all mitochondria have two lipid bilayer membranes: the unwrinkled outer membrane which is permeable to small molecules and ions up to 14 kDa, and the inner membrane which has infoldings called cristae that provide a very large surface area, which is freely permeable to just a few small molecules such as water, O2, CO2 and NH3. The inner membrane also contains the components of the respiratory chain and ATP synthase. Enclosed by the inner membrane is the mitochondrial matrix, which is a water-containing compartment that contains the mitochondrial DNA, ribosomes, granules, and all the pathways of fuel oxidation except glycolysis. These include the pyruvate dehydrogenase complex, the enzymes of the citric acid cycle, and the pathways of fatty acid and amino acid oxidation

19. Mitochondrial dysfunction in cell injury
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Mitochondrial dysfunction in cell injury

20. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Functional and morphologic consequences of decreased intracellular ATP during cell injury

21. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Free radicals
Definition: unstable chemical species with a single unpaired electron in the outer orbital.
1) Reactive nitrite species
2) Oxygen free radicals or reactive oxygen species (ROS) include:
Superoxide anion radicals (O2-)
Hydrogen peroxide (H2O2)
Reactive hydroxyl radical (HO.)

22. Causes and Targets of Cell Injury
Free radicals
Causes and Targets of Cell Injury
Sources & generation
Inflammation
Radiation
Oxygen toxicity
Chemicals
Reperfusion injury
Targets
Antioxidant activity
Dr. Marwan Qubaja / Pathology I
Free radical damage also underlies chemical and radiation injury, toxicity from oxygen and other gases, cellular aging, microbial killing by phagocytic cells (Chapter 9), inflammatory cell damage, tumor destruction by macrophages, and other injurious processes (see Fig. 1-3).

23. Causes and Targets of Cell Injury
Antioxidant activity
Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Free radicals are unstable and generally decay spontaneously
free radicals are inherently unstable and generally decay spontaneously; superoxide, for example, rapidly breaks down in the presence of water into oxygen and hydrogen peroxide. However, cells have also developed several enzymatic and nonenzymatic systems to inactivate free radicals (see Fig. 1-7).
The rate of spontaneous decay is significantly increased by the action of superoxide dismutases (SODs) found in many cell types (catalyzing the reaction 2H → H2O2 + O2).
Glutathione (GSH) peroxidase also protects against injury by catalyzing free radical breakdown ( + 2GSH → 2H2O + GSSG [glutathione homodimer]). The intracellular ratio of oxidized (GSSG) to reduced (GSH) glutathione is a reflection of the oxidative state of the cell and an important aspect of the cell's ability to catabolize free radicals.
Catalase, present in peroxisomes, directs the degradation of hydrogen peroxide (2H2O2 → O2 + 2H2O).
Endogenous or exogenous antioxidants (e.g., vitamins E, A, and C, and β-carotene) may either block the formation of free radicals or scavenge them once they have formed.
Although free ionized iron and copper can catalyze the formation of reactive oxygen species, these elements are usually sequestered by storage and/or transport proteins (e.g., transferrin, ferritin, and ceruloplasmin).
Endogenous or exogenous antioxidants (e.g., vitamins E, A, and C, and β-carotene) may either block the formation of free radicals or scavenge them

24. Causes and Targets of Cell Injury
Chemical injury I
Dr. Marwan Qubaja / Pathology I
Two mechanisms:
Direct combination with a critical molecule of cell component
the greatest damage is sustained by the cells that use, absorb, excrete, or concentrate the compounds.
Examples:
Mercuric chloride poisoning (HgCl2), Hg binds to the sulfhydryl groups of cell membrane proteins, causing inhibition of ATPase-dependent transport and increased membrane permeability.
Antineoplastic chemotherapeutic agents and antibiotics

25. Causes and Targets of Cell Injury
Chemical injury II
Dr. Marwan Qubaja / Pathology I
Activation of an inactive chemical
Many chemicals are not intrinsically biologically active but must be first converted to reactive toxic metabolites by the P-450 oxidases in the smooth endoplasmic reticulum of the liver and other organs.
Involves the formation of reactive free radicals
Examples:
Carbon tetrachloride (CCl4)
Acetaminophen
Carbon tetrachloride (CCl4, used widely in the dry cleaning industry) and acetaminophen belong in this category. CCl4, for example, is converted to the toxic free radical CCl3·, principally in the liver. The free radicals cause autocatalytic membrane phospholipid peroxidation, with rapid breakdown of the endoplasmic reticulum. In less than 30 minutes, there is a decline in hepatic protein synthesis of both enzymes and plasma proteins; within 2 hours, swelling of the SER and dissociation of ribosomes from the RER have occurred. There is reduced lipid export from the hepatocytes, owing to their inability to synthesize apoprotein to complex with triglycerides and thereby facilitate lipoprotein secretion; the result is the "fatty liver" of CCl4 poisoning. Mitochondrial injury follows, and subsequently diminished ATP stores result in defective ion transport and progressive cell swelling; the plasma membranes are further damaged by fatty aldehydes resulting from lipid peroxidation in the SER. The end result can be calcium influx and eventually cell death.
Lipid peroxidation refers to the oxidative degradation of lipids. It is the process whereby free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage. This process proceeds by a free radical chain reaction mechanism.

26. Causes and Targets of Cell Injury
Dr. Marwan Qubaja / Pathology I
Chemical injury II
Example 1:
Carbon tetrachloride (CCl4)
Used in dry cleaning
Converted to the toxic free radical CCl3· in the liver
Carbon tetrachloride (CCl4, used widely in the dry cleaning industry) and acetaminophen belong in this category. CCl4, for example, is converted to the toxic free radical CCl3·, principally in the liver. The free radicals cause autocatalytic membrane phospholipid peroxidation, with rapid breakdown of the endoplasmic reticulum. In less than 30 minutes, there is a decline in hepatic protein synthesis of both enzymes and plasma proteins; within 2 hours, swelling of the SER and dissociation of ribosomes from the RER have occurred. There is reduced lipid export from the hepatocytes, owing to their inability to synthesize apoprotein to complex with triglycerides and thereby facilitate lipoprotein secretion; the result is the "fatty liver" of CCl4 poisoning. Mitochondrial injury follows, and subsequently diminished ATP stores result in defective ion transport and progressive cell swelling; the plasma membranes are further damaged by fatty aldehydes resulting from lipid peroxidation in the SER. The end result can be calcium influx and eventually cell death.
Example 2: