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X Understanding Disease > Xenobiotics > Flashcards

Xenobiotics Flashcards

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1
Q

what is a xenobiotic?

A

Foreign substance with no biological benefit nutritionally

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2
Q

what does Biotransformation mean?

A

xenobiotic metablolism

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3
Q

what does detoxification mean?

A

inappropriate as purpose of metabolism is to ensure excretion and changes in toxicity coincidental

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4
Q

what 5 classes of xenobiotics are there?

A 
Food additives and anutrients
Drugs
Pesticides and herbicides
Industrial chemicals
Bacterial metabolites
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5
Q

what is an example of Food additives and anutrients xenobiotics?

A

Colourings, pigments

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6
Q

what example of drug xenobiotics are there?

A

Aspirin, oral contraceptives

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7
Q

what example of pesticides and herbicides xenobiotics are there?

A

Fly sprays, weed killers

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8
Q

what examples of industrial chemical xenobiotics are there?

A

Dyes, detergents, bleaching agents

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9
Q

what examples of bacterial metabolite xenobiotics are there?

A

Putrescine, other amines

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10
Q

what means of exposure to xenobiotics are there?

A

accidental
coincidental
deliberate

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11
Q

what is an example of accidental exposure?

A

inhalation of garden sprays, oven cleaner, furniture polish etc

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12
Q

what is an example of coincidental exposure?

A

occupational exposure, inhalation of atmospheric pollutants

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13
Q

what is an example of deliberate exposure?

A

applications of cosmetics/deodorant, administration of a drug

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14
Q

what is the mechanism of metabolism and excretion of xenobiotics?

A

1) administration via gut, Lungs, Skin, Parenteral routes
2) direct to tissue retention/metabolism to tissue retention
3) direct to excretion
4) metabolism to excretion
5) excretion can return xenobiotic to Enterohepatic circulation, to return to gut, Lungs, Skin, Parenteral routes

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15
Q

what are the routes of excretion of xenobiotics?

A

urine, bile/faeces, expired air, swear, tears, breast milk

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16
Q

what is the influence of the physical properties of the xenobiotics on excretion?

A

if hydrophillic water soluble: excreted unchanced

if hydrophobic lipid soluble: retained in membrane unchanged

somewhere on spectrum between hydrophillic/hydrophobic: metabolised to increase water solubility to excrete

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17
Q

what happens if the xenobiotic is similar to a natural metabolite?

A
  1. Bind to specific transport/binding proteins in cells/circulation
  2. Enter cells/organelles via specific transporters
  3. Be metabolised by specific enzymes e.g. fluoroacetate -> fluorocitrate
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18
Q

what is the aim of metabolism?

A

increase water solubility for excretion

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19
Q

what is the mechanism of phase 1 metabolism?

A
  • Prepare molecule for phase 2
  • insertion of a reactive group via oxidation, reduction or hydrolysis
  • Usually little change in H2O solubility
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20
Q

what is the mechanism of phase 2 metabolism?

A
  • Attach conjugating group (conjugation) e.g. sulphate
  • Requires energy
  • Usually increases H2O solubility
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21
Q

what 3 enzymes catalyse oxidation?

Study These Flashcards
A

Cytochrome P450 family
Flavin-containing monooxygenases
Prostaglandin synthetase

22
Q

what does the Cytochrome P450 family enzyme do in oxidation?

Study These Flashcards
A

Catalyse insertion of oxygen atom
XH -> XOH
“activate” xenobiotics

23
Q

what does the Flavin-containing monooxygenases enzyme do in oxidation?

Study These Flashcards
A

Mechanism of action similar to P450 family

Fewer enzymes

24
Q

what does the Prostaglandin synthetase enzyme do in oxidation?

Study These Flashcards
A

Catalyses prostaglandin formation

Required electrons derived from various substances including some xenobiotics

25
what is an example of a reduction reaction?
protonsil -> sulphanilamide
26
which groups do reduction reactions usually involve? ?
nitrogen-containing groups
27
what is a typical example of a hydrolysis reaction?
Acetylsalicylic acid (aspirin) + H2O -> Acetic acid + Salicylic acid
28
what 4 types of conjugating groups/reactions are there?
1. Glucuronic acid/glucuronidation 2. Sulphate/sulphation 3. Methyl/methylation 4. Amino acids
29
which conjugating group/reaction reduces H2O solubility? when?
Methyl/methylation when too much paracetamol
30
how is conjugation used to eliminate bilirubin?
(Spleen) Haem catabolism -> Bilirubin (Liver) Bilirubin conjugated to Bilirubin diglucuronide Excretion into bile
31
how is conjugation used to produce bile salts?
(Liver) Cholesterol -> Cholyl CoA Conjugated to Glycocholate/taurocholate
32
what factors affect metabolism?
``` Genetic factors Tissue Sex Stage of development Age Induction Interaction with other xenobiotics, e.g. drugs ```
33
what is the responsiveness to drugs affected by?
genetics - activity of metabolising enzymes
34
how does the pharmacodynamics of CYP2C9 affect drug responsiveness?
CYP2C9 (form of P450) (metabolises warfarin) – individuals with at least 1 copy of allele 2 require 17% less those with at least 1 copy of allele 3 require 37% less, than those homozygous for allele 1 Titrate dose according to enzyme activity
35
why can xenobiotics cause problems in one tissue but not another?
1. Selective accumulation 2. Different route for metabolism 3. Potential for further metabolism
36
what is an example of a xenobiotic causing problems in one tissue but not another?
``` (Liver) 2-Naphthylamine Oxidation N-hydroxy-2-naphthylamine* Conjugation Glucuronide (Bladder) Glucuronide hydrolysed due to low urinary pH ``` N-hydroxy-2-naphthylamine* *Mutagenic
37
why is it harmful in the bladder but not the liver?
liver conjugates it but bladder doesn’t. it builds up in the bladder
38
what happens when there is no metabolism of the xenobiotic?
accumulation
39
what happens when there is partial metabolism of xenobiotic?
accumulation of phase 1 product
40
what happens if a xenobiotic is metabolised via an alternative route? give an example
Can result in selective toxicity and/or mutagenicity if substance that accumulates is harmful e.g. Phenytoin (anti-convulsant) metabolised by prostaglandin synthetase = mutagen in foetal tissues
41
what affect do xenobiotics often have on xenobiotic metabolising enzymes?
often increase activity
42
what non-specific xenobiotic metabolising enzymes are there?
phenobarbital
43
what specific xenobiotic metabolising enzymes are there?
phenylbutazone
44
does interactions does CYP2D6 have with other xenobiotics?
inhibited by fluoxetine -> reduced metabolism of all other drugs metabolised by this enzyme
45
does interactions do Furanocoumarins have with other xenobiotics?
occur specifically in grapefruit | inhibit intestinal CYP3A4 -> increased bioavailability of a number of drugs including some statins
46
what is Phenylbutazone?
an anti-inflammatory agent Induces enzymes for which it is substrate Enzymes also act on warfarin (anti-coagulant)
47
what happens if Phenylbutazone and warfarin are both given together?
must increase dose of warfarin if phenylbutazone withdrawn, must decrease dose of warfarin as induction effect lost
48
what does activation mean?
Enhancement of toxicity &/or mutagenicity as a result of attempts to carry out biotransformation
49
what are the causes of activation?
Metabolism more reactive product and/or Accumulation of reactive metabolite because unable to be metabolised
50
what are the key features of activation?
``` May result from any type of reaction Some enzymes/processes more likely to cause activation especially: Certain forms of cytochrome P450 Prostaglandin synthetase Reduction ```

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