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BI316 > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

What is biotransformation?

A

It is a protective mechanism of the body to remove potentially harmful substances

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2
Q

Disadvantage of biotransformation

A

It chemically modifys xenobiotic substances causes it to loose its pharmacological potency and biological function

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3
Q

Phases of biotransformation reactions:

A

Phase 1 and Phase 2

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4
Q

Phase 1 is biotransformation reactions:

A

Includes oxidation, reduction, alkylation and hydrolytic cleavage

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5
Q

Phase 2 of biotransformation reactions:

A

Includes conjugation reactions with Glucoronic acid, sulfuric acid or peptides

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6
Q

What are xenobiotics?

A

They are potentially harmful substances foreign to a living organism
-At high concentrations and it may interfere with cellular functioning

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7
Q

How can xenobiotics be removed?

A
  1. Direct excretion of the parent substances
    Or
  2. Metabolic bio transformation
    -Phase 1 or Phase 2
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8
Q

Examples of fat soluble toxins:

A

-Drugs
-Food additives
-Pollutant
-Contaminant
-Metabolites
-Alcohol
-Bacterial products

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9
Q

What does biotransformation do to fat soluble toxins?

A

It turns it into water-soluble, polar substances so they are easy to eliminate

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10
Q

Where are biotransformed waste products be removed from?

A

Through the stool or urine

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11
Q

Biotransformation causes what changes in xenobiotics?

A

-Disappearance of original foreign substance
-Loss of biological activity
-Metabolites are usually less toxic
-Polar metabolites are excreted faster

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12
Q

How does phase 1 biotransformation happen?

A

-It is a bioinactivation process (sometimes bio activation)
-The xenobiotics is altered by the introduction of polar groups (hydroxyl, carboxyl and amino)
-This alteration is caused by either oxidation, reduction or hydrolysis

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13
Q

Phase 1 takes place under the influence of what system?

A

The mixed-function oxidase (MFO) system

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14
Q

Mixed-function oxidase (MFO) system:

A

-Consists of the super family CYP450 proteins
-These are drug induced cytochrome (CY) heme proteins found in the smooth ER

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15
Q

Function of CYP450 proteins?

A

-They are critical for drug metabolism
-They work by catalyzing the oxidation of substrates

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16
Q

What is Glutathione?

A

-It is an important component involved in phase 2 biotransformation
-It is a tripeptide with a gamma peptide linkage between the carbonyl group
Of the glutamate side chain and the amine group of cysteine

17
Q

Chemical name of glutathione?

A

Gamma-glutamyl-cysteinyl-glycine TRI-peptide (GSH)

18
Q

Where is glutathione found?

A

It can be found in high concentrations in liver cells

19
Q

What is the major site of biotransformation

A

Liver cells

20
Q

Function of Glutathione transferase (GST) ?

A

It is an enzyme that catalyzes reactions where sulphydryl group (-SH) of GSH acts as a nucleophile binding to electrophiles

21
Q

What are GSH conjugated?

A

-Formed by phase 2 biotransformation reactions
-The conjugates are excreted into bile
-They may be further metabolized to form mercapturic acid derivatives

22
Q

Biotransformation of the xenobiotic Benzene:

A

It undergoes both phase 1 and phase 2 biotransformation

23
Q

Phase 1 biotransformation of Benzene:

A

-In the Mixed-function oxidase it becomes epoxide and then phenol

24
Q

Phase 2 biotransformation of Benzene:

A

The phenol is converted to phenyl glucuronide by the enzyme glucuronyl transferase

25
Q

What are reactive intermediates

A

They are formed during metabolism of xenobiotics
-Can potentially lead to necrosis or cancer

26
Q

Examples of reactive intermediates formed by MFO and what they cause:

A

-Bromobenzene leads to liver necrosis
-Carbon tetrachloride leads to liver necrosis
-Vinyl chloride leads to liver cancer

27
Q

What are Aflatoxins?

A
  • group of mycotoxins produced as secondary metabolites by the fungus Aspergillus
    -Can contaminate human food and animal feed
28
Q

Function of Aflatoxin B1?

A

When it is metabolized by p450 monopxygenase system in the liver it produces a reactive epoxide named Aflatoxin 8,9-epoxide

29
Q

Aflatoxin 8,9 epoxide:

A

-It can form DNA adducts such as Aflatoxin-Guanine which can induce mutations and liver cancer

30
Q

Are aflatoxins safe?

A

No. Large doses can lead to acute poisoning called aflatoxicosis which can cause liver failure, jaundice, lethargy, nausea and death.
They also destroy crops

31
Q

What was the first known cause of human bladder cancer?

A

Exposure to arylamines in industrial settings

32
Q

Where else can arylamines be found?

A

Cigarette smoke and hair sprays

33
Q

Key enzymes involved in biotransformation

A

-MFO (Cytochrome P450-dependent)
-UGT (UDP-glucuronosyl transferase
-NAT (N-acetyltransferase

34
Q

Toxic reactive intermediate:

A

-Hapten formation
-Direct cytotoxic effect
-DNA adduct

35
Q

Hapten formation leads to?

A

Antibody production which can cause cellular damage

36
Q

Direct cytotoxic effect leads to?

A

Cellular injury which leads to necrosis

37
Q

DNA adduct leads to?

A

Mutation which cause cancer

BI316 (6 decks)

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