Understanding Activation And Detoxification Enzymes
In this post, we will discuss a brief, technical basic explanation of activation and detoxification - two major mechanisms in oxidative homeostasis.
In the future, I will update this post with more references, a MOA section, genetics, and clearer plans of action.
Basics Of Detox Phases
Phases I, II, and III do not need to happen in a linear order.
Phase I Basics
Phase I uses something called functionalization (which is adding a functional group) of a toxin to make it more water soluble.
This reaction (through bioactivation/metabolic activation) can create a toxic metabolite that may be more toxic than the original toxin, thus it needs to be handled (more on this described later).
This is where Phase II comes into play...
Phase II Basics
Phase II uses conjugation or non-conjugation methods, which essentially makes everything more water soluble and less toxic (less reactive).
Phase III Basics
Phase III helps with excretion using export pumps to transfer hydrolyzed metabolites out through the kidneys (urine), stool (bile), or sweat.
Activation Vs Detoxification
What Is Activation?
Activation is the ability for toxins (foreign substances) from the environment to turn on genes and enzymes (mostly in the liver and kidneys).
Foreign substances that are Lipophilic (fat soluble) need to be made more Hydrophilic (water soluble) for excretion.
Lipophilic substances get into the cell through;
- Passively - higher levels of toxins in Extracellular Matrix (ECM) create a “pressure” to get into the cell
- Facilitated - uses transporters that require no energy to get into the cell
- Active - similar to facilitated but uses energy for primary (catalyzed by Na+, K+- ATPase) or secondary (electrochemical exchange) transporters
Foreign substances that are already hydrophilic may bypass Phases I and II and go straight to Phase III for excretion.
During activation, toxic metabolites (such as ROS) are created in the process and, for example, are responsible for many of the problems we see from alcohol-induced.
What Is Detoxification?
Detoxificaiton is the process by which taking foreign compounds and making them more water soluble and less reactive.
That means you have to take foreign compounds (or their toxic metabolites from Phase I) and make them more stable (with antioxidant responses, such as NRF2), so they can be readily excreted.
This usually takes place during Phase II with conjugation or non-conjugation enzymes.
Too Much Of One
Healthy people have a proper balance of activation and detoxifciation, as too much of one thing would be bad.
For example, too much activation with little detoxification, and you have the buildup of damaging free radicals.
Too much detoxification has been implicated in cancers.
Some things that can cause this is:
- Loss of conjugations factors (i.e. no more GSH)
- Epigenetics - something that is:
- Causing too much activation
- Inhibition of the start of deactivation
Phase I Enzymes
Functionalization enzymes consist of:
- Aliphatic Hydroxylation
- Aromatic Hydroxylation
Let's go more in depth...
- CYP450 group - heme protein that metabolizes a lot of drugs (see post on CYPs)
- FMO groups - generally converts foreign compounds into harmless, polar metabolites
- Amine Oxidases - such as MAO-A and MAO-B
- breaks down tyramine, phenylethylamine, benzylamine, and phenylpropanolamine
- byproducts are ammonia, hydrogen peroxide and aldehyde
- Lipoxygenases - metabolize chemicals, pesticides, and drugs
- Alcohol Dehydrogenase - ADHs break down alcohols to to aldehydes (toxic) or ketones
- Aldehyde Oxidase - oxidizes aliphatic and aromatic aldehydes
- Xanthine Oxidase - oxidizes aliphatic and aromatic aldehydes
- Peroxidase - Found in tissues with low CYP450 to oxidize phenols and aromatic amines
- Nitroreductases - reduces nitro (−NO2) groups to hydroxyl amines then to amines (−NH2)
- Azoreductases - reduces azo-compounds to produce two amines
- Carboxylesterase - hydrolizes esters and amides
- Epoxide Hydrolase - detoxes electrophilic epoxides generated from oxidative activation
- Oxidative reactions
- Reductive reactions
- Hydrolytic reactions
Phase II Enzymes
- Makes things more polar (more stable in water/less toxic)
- Transfers glucuronic acid to functionalized metabolites
- Accounts for about 35% of drug conjugations
Glutathione S-Transferases (GST):
- Bind to electrophiles (instead of allowing them to bind to oxygen to make ROS)
- Helps transfer glutathione (GSH is produced from g-glutamic acid, cysteine, and glycine) to electrophiles
- Make electrophiles more water soluble
- Can create cysteine or NAC
- from GSH (sulfur) + electrophile (carbon or nitrogen)
- Detoxes aflatoxin B1
- Conjugates really small lipophilic xenobiotics
- Transfer of a sulfonate group (SO3−) to nucleophilic group of foreign compounds
- May make more toxic metabolites though (in some instances)
- Use an acetyl group, which doesn’t make it more water soluble, but does help in excretion
- Acetyl-coa is involved and via PY540, it can cause activation
- Can be dependent on S-adenosyl-methionine (SAM)
- O-methylation, N-methylation, and S-methylation
- Types of methyltransferases
- COMT, TMT, HMNT
- Doesn’t (usually) make xenobiotics more water soluble, but also helps with activation
- Found in mitochondria
- Use Acetyl-CoA
- Work on glycine, glutamine, arginine, and taurine
Quinone Reductase (QR):
- Uses NADPH, H+, and quinone to make quinones hydrophilic
Epoxide Hydrolase (EH):
- Detoxes compounds containing unsaturated carbon–carbon bonds
- Reduce epoxides, which are unstable metabolites from Phase I (CYP450) reactions
- Epoxides are turned into dihydrodiols, which are easily conjugated and excreted
What Are Some Sources Of Foreign Compounds?
Veggies and fruits are normally healthy.
- chemical derivatives are produced when meat or fish is cooked at high temperature.
- Residues of antibiotics and hormones used to raise chickens, cattle, pigs, and sheep remain as contaminants in meat.
- produce secondary metabolites (mycotoxins)
- Mycotoxins - represent a diverse group of chemicals that can occur in a variety of plants used as food such as grains and fruits.
Others in food:
- pesticides from crop sprays
- fungi from storage
- phthalate esters from packaging
- styrene from containers
- contaminated with industrial wastes (e.g., mercury, PCBs, and dioxin)
Drugs and smoking are foreign compounds.
- Industrial combustions in refinery, incineration, and coal plants produce industrial pollution including polycyclic aromatic hydrocarbons, dioxins, and PCBs.
- they are formed when amino acids react with creatine in muscle when meats (beef, pork, or fish) are cooked at high temperature by frying, broiling, or barbecuing.
- Induces CYP1A2
- May be related to cancer, esp when cooked/smoked (such as cigarettes or frying bacon)
- also found in mushrooms, fermented and smoked fish, and pickled foods
PAHs are mutagenic and consumed by eating grilled, charred meats and contaminated foods.
- Dyes are usually nontoxic but the byproducts from breaking it down in the body can be
- 4-Hydroxylnonenal comes from oxidation of lipids or fatty acids
- 4-Hydroxylnonenal can also be produced in foods during processing or storage.
Mycotoxins can get into food.
- common ones are:
- Patulin (in apples)
- Aflatoxin (meats, chicken, turkey)
- Diallyl sulfide helps with this by inhibiting CYP450 and increasing GST
- Dialyl disfulfie helps by increasing GST
- Green tea may help with acetaminophen UDP-GST down regulation
- Phase II inducers (resveratrol) increase resistance to xanthine-mediated effects.
- Benzene causes immune suppression and anemia…phase II inducers help with phenol byproduct but not hydroquinone
- DEHP (a pthalate ester found in PVC vinyl plastics etc) causes human reproductive harm and is metabolized by both Phase I and II
- phase II may help more
- Phase II (sulforaphane) blocks diesel exhaust particles to enhance IgE production (via GST)
- Aresenic requires SAMe before excretion in urine
- Some PCBs can be excreted via conjugation but some persist in the body - major problem
Bioactivation Protection And What To Do
As discussed before high amounts of bioactivation (toxic intermediates) can cause more damage than the original foreign toxic compound.
To protect the body against reactive intermediates we use:
- Conjugation reactions - make more water soluble
- Glutathione - is an antioxidant and helps facilitate excretion (via bile/urine)
- Antioxidant enzymes:
- SOD → converts super-oxide radical to H2O2 + O
- Catalase + glutathione peroxidase → H2O2 + O → H2O + O2
- Vitamin E, C, and b-carotene are small antioxidant molecules can neutralize free radicals by accepting or donating an electron
What To Do?
Inducing Phase II while inhibiting Phase I is usually the best way to protect against activation and enhance detoxification.
Phase I Inducers
- Brussels sprouts
- Mustard seed
- Onion (has shown to induce and inhibit)
- Grapefruit (induces and inhibits)
- Oroblanco (induce)
Stay away from these:
- Acetaminophen - creates highly reactive compounds
- Aflatoxin - creates highly reactive compounds
Bifunctional Inducers raise both Phase I and II:
- Azo dyes
- Polycyclic aromatic hydrocarbons
Phase I Inhibitors
Phase II Inducers
- Brussels Sprouts
- Cruciferous Vegetables (in general)
- Garden Cress
- Green leaf veggies
- Juices (usually)
- Mustard Seed
- Tropical Ginger
- Tonka Beans
- Citrus Fruit (in general)
- Musa x paradisiacal
Monofunctional Inducers only raise Phase II:
- Flavonoids and Isoflavones
- Polyphenols and Phenols
- Garlic - Diallyl sulfide
- Limonene (Lemon and citrus)
- 1,2 -Dithiol-3-thiones
- Quinone reductase is exclusively induced by monofunctional inducers
Phase II Inhibitors
Some Phase II inhibitors
- Cigarette Smoke
- DJ-1 oxidation
- Mold - e.g. Aflatoxins