Detoxification Phases

Question 1

Phase zero

Answer 1

Phase zero = the entry of the toxin into the cell (primarily hepatocytes) or exit of the unmetabolised toxin from storage inside cells such as adipocytes

• Fat-soluble toxins diffuse through the cell membrane.
• Water-soluble or charged toxins need to access or leave the cell through a transporter. The main transporter families used for phase zero are (both with many different transporters):

– Solute carriers (SLC) and ATP binding cassette carriers.

Question 2

Phase I

Answer 2

Phase I = primarily involves transformation enzymes collectively known as cytochrome P450 (CYP450) in the liver

Most toxins that arrive inside the hepatocytes are lipophilic and have to undergo phase I detoxification.

• The CYP450 + toxin / hormone reaction creates an active binding site on the toxin (often exposing an –OH / alcohol group). This makes them more water-soluble, but also more reactive in order for conjugation to occur (phase II)

Question 3

CYP450

Answer 3

CYP450 = involves 50 to 100 enzymes, each of which is best able to detoxify certain compounds, but has broad specificity

‒ Many of the enzymes are produced in response to increased exposure to a certain toxin by producing more of the enzyme that degrades it. This can happen at the expense of other toxin biotransformation.

‒ Induction of phase I enzymes without co-induction of phase II can = increased reactive intermediates, ↑ oxidative stress

Question 4

Phase I to phase II key considerations

Answer 4

• The progression of metabolites from phase I through to phase II must happen in quick succession to minimise damagingeffects of intermediary products.
• Genetic variations (SNPs), diet and availability of nutrient co-factors can influence an individual’s ability to metabolise toxins.
• Phase II enzymes are generally less inducible than phase I.
• Typically, phase I will be upregulated due to toxic load, while phase II will be slow due to overwhelm from heightened phase I activity and / or lack of co-factors (e.g., a poor, nutrient-depleted diet)

Question 5

Supporting phase I detoxification:

Answer 5

Reduce the toxic load to slow phase I:

1. Go organic to minimise intake of pesticides and other xenobiotics from the food chain.
2. Minimise exposure of xenobiotics in toiletries and household products.
3. Stop smoking and avoid caffeine.
4. Avoid chargrilled and smoked foods.
5. Reduce or ideally eliminate alcohol.
6. Avoid unnecessary medications.
7. Avoid use of plastics in contact with food.

Question 6

Co-factors to support phase I detoxification

Answer 6

• The B complex vitamins are vital co-factors for the action of the cytochrome P450 enzymes and other phase I enzyme families.
• Alcohol depletes B vitamins and so should be avoided to optimise an individual’s B vitamin status.
• B vitamin-rich foods include whole grains, legumes, mushrooms, sunflower seeds, pistachios, wild fish, eggs, sea vegetables.
• Adequate amounts of the branched chain amino acids (BCAAs) leucine, isoleucine and valine are also necessary to support phase I activity. Sources include quinoa, fish, eggs and meat.

Question 7

Detoxification Phase I
SNPs

Answer 7

CYP450 genes code for CYP450 enzymes.
- CYP2E1 ― ethanol
- CYP1A2 ― caffeine
- CYP2C9 ― warfarin
- CYP17A1 ― pregnenolone
- CYP19A1 ― testosterone
- CYP1A1 ― oestrogen

SNPs can influence enzyme activity ― either turning it up (↑ metabolism) or down (↓ metabolism)

Question 8

Phase I SNPs of most clinical relevance: CYP1A1
Gene

Answer 8

CYP1A1 gene codes for the phase I enzyme CYP1A1 which is responsible for:

– Deactivating oestrogen. An SNP of this gene increases the risk of oestrogen dominance.

– Detoxifying many toxins including polycyclic aromatic hydrocarbons (PAHs) and solvents.

PAHs damage DNA increasing cancer risk. They are formed in chargrilled meat, smoked foods and cigarettes.

Question 9

Phase I SNPs of most clinical relevance: CYP1A1
SNP

Answer 9

A G2453T SNP at Rs1799814 is associated with reduced activity of CYP1A1

Question 10

CYP1A1 SNP recommendations:

Answer 10

• Avoid (more crucial for these people): Chargrilled

meats and smoked food. Smoking and exposure to second-hand smoke. Industrial pollutants and synthetic oestrogens (e.g., parabens in beauty products, plastic).

• Focus on plant foods (minimal animal protein), rich in colour (phytonutrients) including polyphenols (green tea, berries, apples, etc.). Also rosemary.
• Sulphur-rich foods, especially cruciferous vegetables (e.g., broccoli sprouts for the high I3C content) and allium vegetables).
• Consider supplementation with Indole-3-carbinol.

Question 11

Phase I SNPs of most clinical relevance: CYP1A2:
Gene

Answer 11

CYP1A2 gene encodes a member of the CYP450 family of enzymes, which metabolise nutrients and drugs, including caffeine

Question 12

Phase I SNPs of most clinical relevance: CYP1A2:
SNP

Answer 12

The SNP at rs762551 impacts CYP1A2 activity.

Individuals with the CC genotype, also known as CYP1A2*1C, are ‘slow’ caffeine metabolisers.

‒ Caffeine intake > 300 mg / day can be damaging to the brain, heart, liver and kidneys

Question 13

CYP1A2 SNP recommendations

Answer 13

Avoid all caffeine intake from coffee, tea and foods such as chocolate

Question 14

Phase II

Answer 14

Phase II = a variety of chemical reactions which add functional groups to reactive toxins to make them safe to be released into the blood or bile for excretion via the kidneys or bowel

Question 15

Summary of phase II reactions

Answer 15

Question 16

Glucuronidation:

Answer 16

Question 17

Sulphation:

Answer 17

Question 18

Acetylation

Answer 18

Question 19

Methylation

Answer 19

Question 20

Amino acid conjugation

Answer 20

Question 21

Glutathione conjugation

Answer 21

Question 22

Supporting phase II (increasing Nrf2 gene expression):

Answer 22

• The transcription factor, Nrf2 (nuclear factor erythroid 2) is key to regulating the body’s detoxification and antioxidant system:

– Induction of Nrf2 increases endogenous antioxidants to protect against reactive intermediates, and promotes phase II pathways.

– Nrf2 induction is considered protective against various oxidative stress-related conditions such as cancer, kidney dysfunction, neurological disease, and cardiovascular disease

• Phytonutrients not only scavenge ROS (acting as direct antioxidants), but also regulate Nrf2 activity.
• Phytochemicals / foods that can regulate Nrf2 activity:

‒ Curcumin (turmeric), broccoli constituents, garlic, epicatechins (e.g., green tea), lycopene (tomatoes), resveratrol (e.g., red grapes), isoflavones (legumes, alfalfa sprouts), rosemary, blueberry, pomegranate, naringenin (grapefruit).

‒ The effects of whole foods / herbs versus isolated bioactive compounds appear greater.

Question 23

Phase III

Answer 23

Phase III = the removal and excretion phase where detoxified products are pumped into blood or bile for elimination

This involves over 350 antiporter proteins (ATPdependent pumps) that work on specific substrates

Question 24

Supporting phase III:

Answer 24

‒ Fasting (e.g., intermittent / vegetable broth).

‒ Being in a lipolytic state allows toxins stored in fat cells to be mobilised and eliminated.

‒ Fasts and calorie restriction should be short term (5–10 days) and toxin elimination should be supported with practices such as saunas.

• Certain very high dose isolated phytonutrients appear to inhibit phase III — notably curcumin and epicatechins (in green tea).
  – However, turmeric and green tea are highly valuable to detoxification and antioxidant processes.
  – Focus on dietary inclusion and use of whole plant preparations. Good hydration is essential, helping with elimination.
• Bile production and flow can be supported with choleretic and cholagogue herbs. Dandelion root and globe artichoke leaf provide both actions and are also mild diuretics. Burdock root (e.g., tea) is a cholagogue

Question 25

Bile

Answer 25

A proportion of conjugated metabolites from the liver are pumped into bile and travel to the intestinal lumen for excretion:

• Efficiency of excretion is dependent on different factors, particularly influences from the diet and microflora.
• Fibre binds conjugated xenobiotics, decreases stool transit time and reduces the amount of deconjugating enzymes in the stool.
• Dysbiosis — undesirable bacteria can produce enzymes such as beta-glucuronidase that deconjugate phase II compounds, ↓ elimination.
• Deconjugated xenobiotics re-enter the blood and are sent back to the liver for processing.

Question 26

Overview of Detoxification

Answer 26