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Metabolism in H&D > 11 - Xenobiotic metabolism 2 > Flashcards

11 - Xenobiotic metabolism 2 Flashcards

1
Q

Why do xenobiotics need to be modified to be removed?

A

They are often nonpolar and lilophilic

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2
Q

What does phase 1 metabolism introduce to the xenobiotic?

A

FUNCTIONAL GROUPS

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3
Q

What are the 4 categories of metabolic activity?

A

ultra-rapid metaboliser (↑xenobiotic metabolism)
extensive metaboliser (normal)
intermediate metaboliser
poor metaboliser

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4
Q

What xenobiotics have been linked to increased expression of CYP3A enzymes?

A
  • Indinavir (antiviral)
  • Cyclosporin (immuno-suppressant)
  • Carbamazepine (anticonvulsant)
  • Atorvastatin (HMG CoA Reductase inhibitor)
  • Tamoxifen (anti-hormone)
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5
Q

What do xenobiotics such as St Johns Wort do to the CYP3A gene?

A

Bind to the pregane X receptor (PXR) transcription factor.

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6
Q

How does a ligand cause induction of the CYP3A gene?

A

Interacts with the PXR receptor and the RXR (retinoid X receptor) heterodimer. Leads to upregulation of enzyme production.

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7
Q

Why should grapefruit juice not be taken with Felodipine?

A

Grapefruit juice is a potent CYP3A4 inhibitor (64%)

Elevates felodipine plasma concentration

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8
Q

What are the 2 competing pathways for ethanol metabolism?

A

ADH: High affinity, Low capacity
CYP2E1: Low affinity, High capacity

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9
Q

What is the gene that produces ROS through reduction of O2 and is strongly induced by alcohol?

A

CYP2E1

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10
Q

What are the 3 pathways of paracetamol metabolism?

A

1) Sulfation by PAPS
2) Glucuronidation by UDPGA
3) NAPQI production (toxic) by CYP2E1

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11
Q

What is needed for detoxification of NAPQI?

A

Glutathione

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12
Q

NAPQI is an _____ and will react with nucleophilic centres (e.g. __ groups)
Glutathione (GSH), a _______

A

NAPQI is an electrophile and will react with nucleophilic centres (e.g. SH groups)
Glutathione (GSH), a sacrificial nucleophile

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13
Q

Why is CYP2E1 metabolism of paracetamol reduced when the drug is administered alongside ethanol?

A

Ethanol is a CYP2E1 substrate so competes with other substrates before CYP2E1 is induced

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14
Q

What is the gene that produces ROS through reduction of O2 and is strongly induced by alcohol?

A

CYP2E1

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15
Q

What are the 3 pathways of paracetamol metabolism?

A

1) Sulfation by PAPS
2) Glucuronidation by UDPGA
3) NAPQI production (toxic) by CYP2E1

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16
Q

What is needed for detoxification of NAPQI?

A

Glutathione

17
Q

NAPQI is an _____ and will react with nucleophilic centres (e.g. __ groups)
Glutathione (GSH), a _______

A

NAPQI is an electrophile and will react with nucleophilic centres (e.g. SH groups)
Glutathione (GSH), a sacrificial nucleophile

18
Q

Why is CYP2E1 metabolism of paracetamol reduced when the drug is administered alongside ethanol?

A

Ethanol is a CYP2E1 substrate so competes with other substrates before CYP2E1 is induced

Metabolism in H&D (14 decks)

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