CC: Oxidative Phosphorylation Flashcards
What are the 4 specific ways to disrupt mitochondrial function that we discussed in class?
1) Blocking TCA Cycle or Fatty Acyl ß-Oxidation
2) Ionophoretic/Protonophoretic Uncoupling and Disruption of the MPTP (Membrane Permeability Transition Pore)
3) Direct Inhibition of ETC (poisons)
4) Increased permeability of INNER membrane & loss of electrochemical gradient
What blocks the TCA Cycle?
Step 2) Sodium Fluoroacetate
What causes uncoupling of oxidative phosphorylation?
Ionophores: Pentachlorphenol FCCP DNP (dinitrophenol) Valinomycin
What directly inhibits the ETC?
Poisons, of which there are several, each acting at a different Complex in the chain.
What directly inhibits Complex 1 of the ETC?
Rotenone (derived from Derris root; used as fish poison and insecticide)
Amytal (barbituate)
Piericidin A (antibiotic)
Doxorubicin (Adriamycin®) (chemotherapy but cardiotoxic, binds to cardiolipin)
What directly inhibits Complex 2 of the ETC?
Nothing that we discussed. Complex 2 does not traverse the IMM. Instead, it only comes in contact with the matrix and deals specifically with FADH2.
What directly inhibits Complex 3 of the ETC?
ANTIFUNGALS! and a couple others…
Cadmium (Cd++) Antimycin A (antifungal) Stigmatellin (antifungal) Myxothiazol (antifungal; also Complex I) Azoxystrobin (strobilurin antifungal) Atovaquone (napthoquinone; toxoplasmosis, babesiosis, pneumocystis pneumonia, malaria in the combo drug Malarone)
What directly inhibits Complex 4 of the ETC?
Inorganics:
CO (carbon monoxide)
N3- (azide molecule)
Cyanide (cherry trees, targets respiratory center in CNS)
H2S (swine [poo] lagoons)
Phosphine (from zinc phosphide, a fumigant on farms)
What directly inhibits Complex 5 (aka ATP Synthetase) of the ETC?
Oligomycin
What does Cyanide do to the body?
Bright RED Blood due to the inability of ETC to utilize Oxygen in the blood. Body thinks you need more O2 so tachypnea ensues. DEATH occurs very quickly, VERY toxic.
What are sources of Cyanide?
Cherry Trees (trimmings), Spring Sorghum
How do you Dx Cyanide toxicosis?
> 200 ppm cyanide in forage
1-2ppm in blood or muscle
History of access to sources (cherry trees most common)
How do you treat cyanide toxicosis?
Cyanide binds to iron in Complex 4 so competitively binding it to another iron source, Methemoglobin, will work. SODIUM NITRITE will oxidize hemoglobin to methemoglobin.
SODIUM THIOSULFATE will react as a cofactor with Rhodanese (liver enzyme) to make thiocyanate which is removed in the Urine.
What does sodium fluoroacetate do in the body?
It will dissociate and FluoroAcetate binds OAA becoming FluoroCitrate which then binds irreversibly to ACONITASE enzyme (Step 2). Inhibiting ACONITASE inhibits the entire TCA Cycle.
What tissue is most susceptible to sodium fluoroacetate toxicity in the Dog and Cat?
Dog CNS Cat HEART
What are the tissues most susceptible to mitochondrial problems?
CNS and PNS, Cardiac Muscle (Heart), Skeletal Muscle, Kidney Proximal Tubules, Pancreatic ß-cells
What is bright red blood pathognomonic for?
Cyanide toxicosis
What is the mechanism by which ionophores uncouple oxidative phosphorylation?
They disrupt the chemiosmotic gradient by binding ions or protons in the intermembrane space, making them neutrally charged and capable of crossing the inner mitochondrial membrane into the matrix. Once there, it drops off its acquired ion and shuttles back across the IMM. Rinse, repeat, and refuck up the ETC.
What does uncoupling oxidative phosphorylation do to the body?
HEAT PRODUCTION and no ATP. Symptoms include hyperthermia, muscle weakness, tachypnea, and possible convulsions.
What are examples of Protonophores?
Pentachlorophenol, Dinitrophenol (DNP), Dinitrocresol, CCCP, FCCP
What are some other ionophores and what is their mechanism?
Aculeximycin (Pi/H+ symporter; antibiotic)
Valinomycin (K+ ionophore; antibiotic)
Nigericin (K+/H+ antiporter; antibiotic)
What are examples of substances that create pores in the IMM?
Gramicidin (H+ pores; topical antibiotic)
Thermogenin
When is uncoupling of oxidative phosphorylation beneficial?
HEAT Production: Cold adapted animals; Brown Fat in BABIES and HIBERNATING animals
What disrupts the electrochemical gradient via the MPTP?
Free Radical Production; Lipid Peroxidation (change in membrane lipids, creating pore)
Interference with Ca++ (and other ions)
ROS or Ca++ can open MPTP allowing Ca++ to flood the cell. H+ also comes through. Cyt C is also released to Cytosol, activating Apoptosis cascade
What is unique about the MPTP’s structure?
It spans BOTH the Inner and Outer Mitochondrial Membranes
What happens when the MPTP is opened pathologically?
Osmotic swelling of the matrix, loss of electrochemical gradient and potential, release of executioner molecules (caspase activators/Cyt C/ Complex 2)
ATP LOSS!!
What happens to a cell if the ATP loss is moderate when the MPTP is opened? and if it is a severe loss?
Moderate => Apoptosis
Severe => NECROSIS
When would we see ionophores causing problems in the Veterinary world?
Used as coccidiostats
Used to increase feed efficiency in ruminants.
What are some common ionophores used in veterinary medicine?
Monensin (Rumensin)
Lasalocid (Bovatec)
Why would using antibiotics be beneficial to increase rumen feed efficiency?
Certain antibiotics target bacteria/microbes that do not produce proprionate, which is what ruminants use to make Glucose. Piece the rest together.
Name the species in which ionophore toxicity is seen most commonly.
Most common in Horses with Monensin and Sheep.
What are the target organs of ionophore toxicity?
HEART and SKELETAL MUSCLES – ton of mitochondria in these tissues
What are some signs of ionophore toxicity?
Sweating, Pale and Flabby Heart, Hydrothorax, Ascites, Tachychardia and a visible jugular pulse
Liver with White Streaks grossly apparent.
What is some clinical pathology of ionophore toxicity?
Increased muscle enzymes present in the blood:
CK (creatine kinase), AST(aspartate transferase), LDH (lactate dehydrogenase)
increased LDH and CK in pericardial fluid/ECG abnormalities
decreased serum Vit A & E – lipid peroxidation
How do you treat for ionophore toxicity?
REST for up to 6 weeks Activated charcoal to bind ionophores and potential endotoxins Fluids Steroids Vit E/selenium for free radicals
Why were people so happy when DNP hit the market?
Infamous weight loss drug. Continually burn fat but cannot make ATP so deadly consequences.
What are symptoms of Cyanide toxicity?
Excitement, Polypnea and Dyspnea (breathing quickly then slowly), Convulsions, BRIGHT RED MUCOUS MEMBRANES, Mydriasis, Salivation, Muscle Tremors, congested lung, bitter Almond or Bleachy odor
What does H2S/hydrogen sulfide smell like?
Rotten eggs
What is the overall mechanism of action of ionophores?
Eventually Increased net influx of Ca++ leading to damage of mitochondria resulting in Muscle (cardiac and skeletal) necrosis
What are symptoms of ionophore toxicity?
Quick Onset 1-5 days; Immediate Anorexia, Sweating (they’re HOT!), Laying down, colic (as usual), Ataxia, Diarrhea, Hind limb abduction and weakness, Depression, lethargy, Polyuria, Tachycardia, hydrothorax, flabby and pale heart
What tissues are most affected in the horse from ionophore toxicity?
Cardiac and Skeletal Muscle
