L8 Mitochondrial Pharmacology Flashcards
4 main compartments of mitochondria
- outer membrane
- inner membrane space
- inner membrane (folded into cristate, machinery for OXPHOS)
- matrix (location for metabolic reactions)
How many genes does mtDNA encode?
37 (of which 13 are involved in the synthesis of subunits of respiratory chain)
3 main roles of mitochondria
- Energy production by OXPHOS
- Central carbon metabolism
- Biosynthesis of intermediates for cell growth & function
What are primary mitochondrial diseases?
A group of rare genetic metabolic disorders caused by mutations in nuclear or mitochondrial DNA, which result in malfunctioning mitochondria
Mutations in mtDNA only affect…
the integrity of the respiratory chain
Mutations in nuclear DNA disturb…
OXPHOS by impairing mitochondrial protein import, translation & assembly
When do secondary mitochondrial diseases occur?
When other pathological processes negatively impact mitochondrial homeostasis (age-related conditions e.g. neurodegeneration, metabolic disorders, HF)
Main role of mitochondria
energy production
OXPHOS can be divided into 2 basic parts. What are they?
The redox steps (ETC) and the energy-generation events (chemiosmosis)
Main steps of oxidative phosphorylation
- Delivery of electrons by NADH and FADH2
- Electron transport and proton pumping
- Splitting of oxygen to form water
- ATP synthesis
Complex I donates its electron (from NADH) to __
coenzyme A
FADH2 donates its electron to __
Complex II
Coenzyme A donates electrons to __
Complex III (cytochrome C oxidoreductase)
Oxygen collects electrons from __
Complex IV
Mitochondrial membrane potential is vital for…
maintaining the physiological function of the ETC to produce ATP
Significant loss in mitochondrial membrane potential results in…
depletion in cellular energy and subsequent cell death
Mitochondrial dysfunction causes significant changes in __ and __
cellular energy metabolism and ROS generation
Examples of harmful consequences of excessive mitochondrial ROS production
- lipid oxidation
- mtDNA/RNA damage
- protein oxidation
- Ca²⁺-dependent activation of MPTP
- cytochrome C release
Cytochrome C release from mitochondria will induce __
apoptosis (via activation of the intrinsic pathway)
Mitochondrial homeostasis is preserved by the fine coordination between two opposing processes:
- Generation of new mitochondria by mitochondrial biogenesis
- Removal of damaged mitochondria by mitophagy
What are the consequences of mitochondrial biogenesis?
- Increased OXPHOS capacity
- Diminishment of pathological oxidative stress
- Repair of mitochondrial-associated dysfunction
Important stimulant of mitochondrial biogenesis
PGC1α
Mitochondrial dynamics
Fusion and fission
Mitochondrial fusion is regulated by…
proteins such as mitofusins (MFN1 and MFN2) and optic atrophy protein 1 (OPA1)
Mitochondrial fission is controlled by…
proteins such as dynamic-related protein (DRP1)
Difference between mitochondrial fusion and fission
Fusion usually results if there are defective elements in each mitochondrion, which leads to replication of mtDNA during biogenesis. Whereas fission does not involve replication, mtDNA from each mitochondrion is used.
Rationale for targeting mitochondria
Common patterns of how dysfunctional mitochondria contribute to pathogenesis of secondary diseases:
- Excessive ROS
- Disrupted Ca²⁺ homeostasis
- Defective mito biogenesis
- Disrupted mito dynamics
- Inappropriate apoptosis
- Reduced NAD⁺
- Alterations in mito signalling pathways
6 potential therapeutic strategies for how small molecules can affect mitochondria (either directly or indirectly)
- OXPHOS modulators
- Repairing or preventing damage
- Inducing mitochondrial biogenesis
- Enhancing quality control by stimulating degradation of damaged mitochondria
- Co-opting mitochondrial function to induce cell death
- Altering mitochondrial signalling
A widely used approach to target mitochondria is to utilise…
the mitochondrial membrane potential, which drives the accumulation of lipophilic cations within mitochondria
Example of a lipophilic cation that’s able to pass through biological phospholipid bilayers
Triphenyl-phosphonium (TPP)
By conjugation to TPP, bioactive molecules can be…
delivered into the mitochondrial matrix in vivo, provided they are not too polar
Greatest focus of directly-targeted mitochondrial therapeutics
OXPHOS modulators
Examples of OXPHOS modulators
- Idebenone (Raxone)
- Imeglimin
What is Idebenone?
- synthetic short chain analogue of coenzyme Q10 with enhanced solubility & PK
- lipophilic electron carrier (predicted to act as an antioxidant in transfer of electrons from Complex II to III)
Idebenone had disappointing results in clinical trials for which indications?
Alzheimer’s disease and Friedreich’s ataxia
Idebenone has promising initial results for treatment of __
Leber’s hereditary optic neuropathy (LHON) - primary mito disease (vision loss due to mutations in mtDNA)
Idebenone is under review by EMA for treatment of…
DMD patients who are not using glucocorticoids
Preclinical evidence has shown that Imeglimin is…
A competitive inhibitor of Complex I and restores the hyperglycaemia-induced reduction in Complex III content and activity. This lowers reverse electron flow-associated ROS production and improves mitochondrial respiration.
Targeting mitochondrial pyruvate carrier (MPC) controls…
import of pyruvate into matrix from inner mitochondrial membrane, linking glycolysis to OXPHOS
Dysregulated mitochondrial pyruvate uptake plays an important role in…
non-alcoholic fatty liver disease (NAFLD) - secondary mito disease
Pharmacological inhibition of MPC is now being explored as a potential therapeutic to correct mitochondrial dysfunction in __
NAFLD
__-sparing glitazone derivatives have been developed to improve the therapeutic effect of glitazone in non-alcoholic steatohepatitis (NASH) patients specifically through inhibition of MPC.
PPAR𝛾
A burst of __ from mitochondrial respiratory chain upon reperfusion initiates a cascade of tissue damage
superoxide
Mitochondrial dysfunction is a key component of __
heart failure
Mitochondrial antioxidants have had disappointing results in __
CVD
Drugs to protect mitochondria
- Antioxidants to reduce oxidative damage
- Replenish NAD⁺ stocks (nicotinamide)
- Develop drugs to activate chaperones or proteases within mitochondria
Drugs to induce mitochondrial biogenesis
- PPAR𝛾 can be activated directly by pioglitazone, which increases PGC1α expression
- Pioglitazone metabolite, Leriglitazone, in Phase II/III trial for Friedreich’s ataxia - Activation of AMPK can indirectly activate PGC1α
- PXL770 (AMPK activator) in Phase II trial for NASH
Cancer cells can evade death owing to defective induction of the mitochondrial __ pathway by over-expressing __ .
apoptotic
BCL-2
Mitochondrial apoptosis is induced by…
mitochondrial outer membrane permeabilisation (MOMP) and the subsequent release of pro-apoptotic factors such as cytochrome C into the cytosol
What pro-apoptotic proteins form the MOMP pore?
BCL-2 associated X (BAX) and BCL-2 homologous antagonist/killer (BAK)
Example of a BH3-only pro-apoptotic protein
BID
An example of a BH3 mimetic drug that counteracts the suppression of apoptosis in cancer cells by excess BCL-2 anti-apoptotic members
Venetoclax
Venetoclax administered with __ is an effective treatment for CLL
Obinutuzumab (anti-CD20 mAb)
The antioxidants with the highest therapeutic potential target…
glutathione (GSH) and thioredoxin (Trx) redox systems
Novel antioxidant agent that targets the Trx system to reduce ROS-induced cell death
Sonlicromanol
Sonlicromanol recently granted orphan drug designation for __
maternally inherited diabetes and deafness/MIDD (caused by a mutation in mtDNA)
