Lecture 13: Enzyme Induction in Drug Metabolism Flashcards
(25 cards)
How were cytochrome P450 enzymes discovered?
Using spectrophotometry at 450 nm, where CO bound to reduced Fe²⁺ in CYP450, giving a distinct absorption peak.
What happens when a drug induces CYP450 enzymes?
Increases expression of the enzyme, leading to faster metabolism and reduced drug efficacy over time.
Which drug is a classic CYP inducer and how does it work?
Phenobarbitone – induces CYPs, increases ER, RNA, and protein levels gradually over days.
What is the effect of enzyme induction on drug clearance?
Faster metabolism → reduced drug duration/effect.
What are knockout (KO) mice used for in enzyme induction studies?
To remove specific genes (e.g. PXR) and observe if induction fails.
What are knockin (KI) mice used for?
Human genes (e.g. hPXR) are inserted to study human drug responses in mice.
What receptor is associated with CYP3A induction?
Pregnane X Receptor (PXR)
What are the key receptors for CYP gene regulation?
AhR, CAR, PXR, PPARα, LXR/FXR
What do nuclear receptors do when activated?
They bind ligands, dimerize, and bind response elements to activate gene transcription.
What is a response element?
A DNA sequence where nuclear receptors bind to regulate gene expression.
How does the AhR receptor induce CYP1A1?
TCDD binds AhR → translocates to nucleus → binds XRE1 → activates transcription of CYP1A1.
What method measures mRNA induction levels?
Northern blotting – detects specific mRNA bands.
What is EMSA used for?
To detect DNA–protein interactions by observing shifted bands in gel electrophoresis.
What is the principle of promoter reporter assays?
Attach gene promoter to a reporter gene (e.g. luciferase) to detect transcriptional activity.
What is rifampicin’s effect on oral contraceptives?
Induces liver enzymes → increases pill clearance → reduces efficacy.
Why does theophylline clearance increase in smokers?
Induction of CYP enzymes by polycyclic aromatic hydrocarbons (PAHs) in smoke.
What are the 4 mechanisms of enzyme induction?
↑ transcription, ↑ mRNA stability, ↑ translation, ↑ protein stability.
Which of the following is the most likely outcome of CYP3A4 induction by rifampicin?
A. Increased drug half-life
B. Reduced drug metabolism
C. Increased drug clearance
D. Reduced enzyme expression
C
What does the 450 nm absorption peak represent in the discovery of CYP450 enzymes?
A. Oxidised Fe³⁺ binding CO
B. Haemoglobin-oxygen binding
C. Reduced Fe²⁺ binding carbon monoxide in CYP450
D. Free porphyrin ring absorption
C
What is the main purpose of using KO and KI mice in enzyme induction studies?
A. To study gene silencing
B. To measure protein denaturation
C. To evaluate human gene response in a mouse model
D. To suppress drug metabolism
C
Which receptor is activated by polyaromatic hydrocarbons to induce CYP1A1 expression?
A. CAR
B. PPARα
C. AhR
D. FXR
C
What happens when CYP enzymes are induced by long-term barbiturate use?
A. Drug accumulation
B. Enzyme inhibition
C. Enhanced metabolism and tolerance
D. Inhibition of liver metabolism
C
Which of the following best describes a nuclear receptor response element?
A. Sequence bound by tRNA
B. Part of ribosomal RNA
C. DNA motif where receptor dimers bind to regulate transcription
D. Area of the promoter that inhibits gene transcription
C
Which of the following is not a mechanism of enzyme induction?
A. Increased transcription
B. Inhibition of translation
C. Increased protein stability
D. Increased mRNA half-life
B
