In module 1 of this 8-part series on detoxification, you will learn about the 3 phases of detoxification that your body must go through to effectively excrete environmental (exogenous) and metabolic (endogenous) toxins. Stimulating phase 1 detoxification without also promoting phase 2 and phase 3 detoxification can result in harmful reactions as well as failure to excrete the toxic substances. Learn which foods, nutrients, and chemicals stimulate or inhibit each phase and empower yourself with knowledge so that you don’t harm yourself by engaging in a “cleanse” program that only stimulates phase 1 detoxification!
The Phases of Detoxification
Physiology and Biochemistry of Biotransformation and Detoxification
Polymorphism
Single Nucleotide Polymorphism (SNP)
Detoxification and Biotransformation Mechanisms
Phases of Detoxification/Biotransformation
The Regulation of Detoxification
Induction (inducers) of Detoxification
Inhibitors of Detoxification
Nutrients that Support Detoxification
Summary
Physiology and Biochemistry of Biotransformation and Detoxification
The origin of toxins that are present in our bodies comes from an array of sources. These sources include environmental exposure (exogenous sources), such as in the air we breathe, the food we eat, the water we drink, and medications. Endogenous sources of toxins include the products produced by digestion, energy metabolism, tissue regeneration, and end products from the metabolism of hormones, bacterial by-products and other complex molecules.
Detoxification is the process of transforming and removing potentially harmful products from the body. The detoxification process has its own energy, nutrient and regulatory requirements. The process of transforming toxins into a form suitable for excretion is called biotransformation. Biotransformation is the sum of all chemical processes of the body that modify endogenous or exogenous chemicals.
Biotransformation is not only affected by the type of toxicants, but also by the uniqueness of the individual. Individual factors that affect biotransformation include age, sex, body composition, pre-existing pathologies (health imbalances), concomitant disease, nutritional status, genetic predisposition, diet, environmental factors (home environment and occupational factors), medications, and enzyme induction and enzyme inhibition. Enzymes for biotransformation reactions are found in many tissues of the body with the liver being the primary source. The other tissues include the kidneys, the lungs, the intestines and the skin. Biotransformation of a toxin occurs in several steps.
Although it is the largest organ of the human body, skin is often not considered in discussions of drug metabolism. However, there is growing evidence that most common drug-metabolizing enzymes are expressed in the skin. In this module, I will discuss evidence for expression of cytochrome P450, flavin monooxygenases, glutathione-S-transferases, N-acetyltransferases, and sulfotransferases in human skin and skin cells. Additionally, I will discuss the evidence of actual metabolism of drugs.
[Xenobiotic is defined as a chemical or molecule that is foreign to the biological system. These chemicals and molecules can originate from the environment, or from food and metabolic byproducts.]
There is a significant amount of genetic variation in detoxification and biotransformation function; therefore, defining genetic polymorphism is paramount.
DNA does not directly exert its influence on cells, but merely contains sequences of nucleotides known as genes that serve as templates for the production of another nucleic acid known as RNA. The process of reading DNA and writing the information as RNA is termed transcription. The RNA serves as a messenger from the nucleus to the cytoplasm. In the cytoplasm, the RNA is read, and the information is written down as protein. The production of proteins from RNA is termed translation.
The overall process looks like this: DNA→ RNA→protein
This unidirectional flow equation represents the Central Dogma (fundamental law) of molecular biology. This is the mechanism whereby inherited information is used to create actual objects, namely enzymes and structural proteins. An exception to the Central Dogma is that certain viruses (retroviruses) make DNA from RNA using the enzyme reverse transcriptase.
Ref: NIH/www.genome.gov
The genome is the entirety of an organism’s hereditary information. Over 99 percent of the human genome is identical in all humans. It is the other 1 percent that represents the broad variations in human traits, abilities and risk of disease. The gene is the basic unit of inheritance. Genes hold the information to build and maintains the organism’s cells and pass genetic traits to the offspring. Genes are passed from parents to offspring and contain the information needed to specify traits. Genes are arranged, one after another, on the chromosomes. A chromosome is an organized package of DNA found in the nucleus of the cell. Humans have 23 pairs of chromosomes. Each parent contributes one chromosome to each pair so that the offspring get half of their chromosomes from their mother and half from their father. A chromosome contains a single, long DNA molecule, only a portion of which corresponds to a single gene. Humans have approximately 23,000 genes arranged on their chromosomes.
Ref: NIH/www.genome.gov
An allele is one of two or more versions of a gene. An individual inherits two alleles for each gene, one from each parent. If the two alleles are the same, the individual is homozygous for that gene. If the alleles are different, the individual is heterozygous.
Polymorphism
Polymorphism involves one of two or more variants of a particular DNA sequence. The most common type of polymorphism involves variations at a single base pair. Polymorphisms can also be much larger in size and involve long stretches of DNA.
Single Nucleotide Polymorphism (SNP)
Called a single nucleotide polymorphism, or SNP (“snip”), researchers are studying how SNPs in the human genome correlate with disease, drug response, and other phenotypes. There are approximately 1.42 million SNPs in the human genome1. SNP’s may or may not have clinical significance. A SNP can change an amino acid in the protein coding sequence, thereby altering an enzyme binding site and / or the substrate binding site, which will affect the overall function.
[All DNA is composed of a purine base (adenine and guanine) and a pyrimidine base (cytosine and thymine). The bases combine with the sugar, deoxyribose and phosphate to form the four nucleotides (A, G, C, and T)]
Genetic polymorphisms can be the result of chance, or may have been induced external factors, such as radiation or viruses. If a disease process is associated with a polymorphism, it may be termed a genetic mutation. Genetic polymorphisms in biotransformation/detoxification may play a significant role in the pathophysiology of certain diseases.
In the genes coding for certain biotransformation/detoxification enzymes, several polymorphisms have been described, resulting in enzymes with reduced or enhanced activity. As chemical and oxidative stress may be involved in the etiology of Crohn’s disease, polymorphic genes encoding for biotransformation enzymes may be putative candidates for genetic susceptibility to Crohn’s disease.
Detoxification and Biotransformation Mechanisms
Mechanisms that protect human tissue from toxicity include barriers to penetration, mobilization and excretion.1 Metabolic biotransformation produces more easily removed chemicals derivatives via gastrointestinal tract, kidney, skin and lungs.
In its basic from, the way the body processes xenobiotics is illustrated below..
The following illustration outlines the dynamic body systems interaction of toxicants, which include exposure, uptake, transport, storage, metabolism and excretion.
The detoxification process involves the biotransformation of non-polar (lipophilic) toxins into polar (hydrophilic) non-toxic metabolites. These metabolites are eliminated by the liver (bile into the GI tract), kidneys, lungs and skin. The detoxification of toxins occurs in two phases, however a third phase is also said to occur. A system of enzymatic reactions is involved in the process of detoxification.
Phases of Detoxification/Biotransformation
Phase I:
Phase I adds or uncovers a reactive group on the toxin making it more polar, however it may not be fully water soluble, and therefore ready for elimination. In fact, the toxin may be more chemically reactive (reactive intermediate metabolites and/or reactive oxygen species), and therefore more toxic. Phase I reactions consist of oxidation, reduction, dehalogenation, and hydrolysis. These reactions convert molecules into substrates for the Phase II enzymes.
Phase I enzyme system is mainly composed of cytochrome P450 (CYP or CYP450) supergene family. (The P stands for pigment and the 450nm is the wavelength of light absorption). CYP450 is also known as NADPH-CYP450 system because it uses oxygen and the co-factor NADPH. CYP contains an iron protoporphyrin prosthetic group (heme).The cytochromes catalyze a variety of reactions including epoxidation, N-dealkylation, O-dealkylation, S-oxidation and hydroxylation. In addition to detoxification, the cytochromes are important in steroid, cholesterol, and vitamin D synthesis.
The classic reaction is as follows: NADPH + H+ + O2 +RH → NADP+ + H2O + R-OH
(RH is the contaminant)
Cytochromes are primarily located in the smooth endoplasmic reticulum (microsomal fraction) and some are located in the inner mitochondrial membrane. There are numerous isoforms (mixed function oxidases) of CYP450. (An isoform is a cytochrome enzyme variant that derives from a particular gene.)They are classified according to the similarities of the amino-acid sequences. It’s important to note that some cytochrome metabolize very few toxins, while some metabolize multiple. There are over fifty human genes coding for the various cytochrome P450 enzymes. There are several isoforms that are of particular important due to their involvement in metabolism of drugs and other exogenous substances. These include:
CYP3A4
CYP3A5
CYP2D6
CYP2C9
CYP2C19
CYP2C8
CYP1A2
CYP2E1
CYP2A6
The activity of the cytochrome enzymes may differ due to genetic polymorphisms. From a clinical perspective, the differences can have profound clinical consequences when prescribing pharmaceutical, botanical and supplements. A genetic polymorphism can cause reduction in the ability to detoxify a certain chemical or chemicals. The term “slow metabolizers” has been applied to these individuals. (There can also be polymorphisms in the Phase II enzymes). Patient with polymorphisms usually have difficulty clearing medications. This may factor into the numerous adverse drug reactions. The end result of Phase I metabolites are:
Inactive
Equally active
More active
Toxic
Activated (pro-drug)
Phase II
Phase II reactions involve the process of conjugation of the Phase I molecules making them water-soluble, and therefore amenable for elimination. These products are then excreted into the bile and urine.
Phase II conjugation reactions include:
Glucuronidation
Glutathione transferases
S-Methylation
N-Methylation
Acetylation
Sulfotransferases
Thioltransferases
Glycination (peptide bond formation) (Amino acid conjugation)
All of these reactions require energy (ATP) and cofactors to proceed.
Phase III (The Antiporter System)
Phase III has also been called the antiporter system. A transmembrane protein pump called p-glycoprotein appears to be responsible for “pumping” xenobiotics out of the cell in an effort to decrease their intra-cellular concentration. Antiporter activity has also been associated with the Phase I enzyme CYP3A in the intestines. The antiporter system in the intestine pumps xenobiotics back into the intestinal lumen for elimination. The system has also been associated with multiple drug resistance.
The Regulation of Detoxification
The activity of the enzymes involved in detoxification are either induced or inhibited by a number of factors which include genetics, diet, environment toxins, medication, and nutritional status.
Induction (inducers) of Detoxification
Certain substances can cause the upregulation of Phase I enzymes without the corresponding upregulation of the Phase II enzymes. If Phase I enzymes are upregulated or induced without an increase in Phase II activity, the result will be an increase in oxidative stress due to the fact that the intermediate metabolite can be more toxic than the original compound that activated the Phase I enzymes. An example of this is the polycyclic hydrocarbons from cigarette smoke that induce CYP1A2. Another example is the drug phenobarbital, which induces CYP2B6.
Substances that induce Phase I include:
Drugs; nicotine, alcohol, phenobarbital, steroids, sulfonamides
Foods; cabbage, broccoli, high protein diet,
Environmental toxins; exhaust fumes, paint fumes, dioxin, pesticides, charbroiled meats
Nutrients ; see list below
Inhibitors of Detoxification
The enzyme systems of Phase I and Phase II can be inhibited by several mechanisms, which include medications, foods, nutrient deficiency and botanicals. An example of a food causing inhibition of detoxification is grapefruit, which inhibits CYP3A4.
Substances that inhibit Phase I:
Drugs; see list below
Foods; grapefruit (naringenin), curcumin(also stimulates Phase II)
Bowel dysbiosis
The following is a list of CYP450 Substrates, Inhibitors and Inductors:
(A substrate is a molecule upon which an enzyme acts)
CYP450 SUBSTRATES
1A2
amitriptyline clomipramine imipramine
fluvoxamine duloxetine mirtazapine
chlorpromazine fluphenazine haloperidol perphenazine clozapine olanzapine ziprasidone
ropinirole
ALL methylxanthines
2B6
selegiline
bupropion
methadone
2C19
amitriptyline clomipramine imipramine
diazepam
phenytoin phenobarbital
citalopram escitalopram fluoxetine sertraline venlafaxine
PPIs
2D6
tranylcypromine meclobemide
amitriptyline clomipramine desipramine doxepin imipramine nortriptyline
citalopram fluoxetine escitalopram paroxetine nefazodone trazodone duloxetine venlafaxine
chlorpromazine fluphenazine haloperidol thioridazine perphenazine aripiprazole clozapine quetiapine risperidone
metoprolol most beta blockers
codeine hydrocodone prodrug dextromethorphan tramadol prodrug
tamoxifen prodrug
ondansetron
3A4
amitriptyline clomipramine doxepin imipramine
buspirone citalopram escitalopram paroxetine sertraline mirtazapine nefazodone trazodone venlafaxine
chlorpromazine haloperidol perphenazine pimozide aripiprazole clozapine quetiapine risperidone ziprasidone
triazolo- benzodiazepines zaleplon zolpidem zopiclone
carbamazepine valproic acid
buprenorphine codeine fentanyl hydrocodone prodrug meperidine methadone tramadol prodrug
statins exceptions pravastatin and rosuvastatin
antiarrhythmics
CCBs beta blockers
macrolide azithromycin
CYP450 INHIBITORS
1A2
amitriptyline imipramine
fluvoxamine duloxetine
ciprofloxacin norfloxacin ofloxacin
cimetidine
2B6
fluvoxamine
clopidogrel ticlopidine
2C19
amitriptyline imipramine
fluoxetine fluvoxamine paroxetine
PPIs †
ketoconazole
† lansoprazole is the most potent in vitro inhibitor of 2C19
2D6
All TCAs
fluoxetine paroxetine bupropion sertraline > 100-150mg duloxetine fluvoxamine citalopram
chlorpromazine fluphenazine haloperidol perphenazine thioridazine aripiprazole clozapine risperidone
methadone
valproic acid mild
*quinidine* ritonavir cimetidine diphenhydramine Vistaril
Metoclopramide
3A4
nefazodone norfluoxetine fluoxetine fluvoxamine
haloperidol pimozide
ciprofloxacin norfloxacin
keto- and itraazole
diltiazem verapamil
cimetidine protease inhibitors NNRTIs
Grapefruit
CYP450 INDUCERS
3A4
carbamazepine oxcarbazepine topiramate >200mg
phenobarbital phenytoin
rifampin ritonavir efavirenz St. John’s Wort modafinil
2D6
No Inducers!
2C19
carbamazepine valproic acid
pnenonobarbital
phenytion rifampin
rifampin
2B6
phenobarbital
cyclophosphamide
1A2
modafinil
cruciferous vegetables charbroiled foods
cigarette smoke
Nutrients that Support Detoxification
Phase I
Thiamine
Riboflavin
Niacin
Folic acid
Vitamin C
Flavinoids
Phospholipids
Indoles
Pyridoxine
Cobalamin
Iron ,zinc, selenium, magnesium
Nutrients that support intermediate metabolites (between Phase I and Phase II)
Antioxidants in general (vitamin A,C,E)
Flavinoids
Coenzyme Q10
Phase II
Flavinoids
Indole-3 carbinol
Carnosic acid
Isoflavinones
Ellagic acid
Garlic
Specific Phase II nutrients, (Inducers) and [inhibitors];
Glutathione conjugation – glutathione, B6, NAC (Inducers-Brassica family, dill, caraway); [Inhibitors – deficiencies of selenium, B12, zinc and glutathione]
Amino Acid conjugation – glycine (Inducers – glycine); [Inhibitors – low protein diet]
Methylation – S-adenosyl-methionine (Inducers – Lipotropic nutrients – choline, methionine, betaine, folic acid, and B12); [inhibitors – deficiency of B12 or folic acid]
Sulfation – cysteine, methionine, molybdenum (Inducers – cysteine, methionine, taurine); [inhibitors – NSAIDS, molybdenum deficiency, tartrazine(yellow food dye)]
Acetylation –Acetyl-CoA, B5 [inhibitors – deficiency of B2, B5, or C]
Glucuronidation – glucuronic acid (inducers- fish oils); [inhibitors – probenicid, aspirin]
[note that the Brassica family (broccoli, cabbage and brussel sprouts) stimulate both Phase I and Phase II]
Summary
The detoxification/biotransformation process is extremely complex. The interactions between Phase I and Phase II , as well as your own unique biochemistry, are the most important factors to address when evaluating your ability to detoxify. Optimal health requires a balance between all of the phases of detoxification, as well as optimal gastrointestinal function.
References
1. Biotransformation of Drugs in Human Skin, Svensson, CK, PubMed, J.S. National Library of Medicine National Institutes of Health, Drug Metab dispos, 2009 Feb:37(2):247-53, Epub 2008 Nov 12
2. Genetic Polymorphisms in Biotransformation Enzymes in Crohn’s Disease: Association with Microsomal Epoxide Hydrolase, D.J. deJong, EMJ van der Logt, A van Schaik, HMJ Roelofs, WHM Peters, THJ Naber, Gut 2003;52:547-551
3. Laboratory Evaluations for Integrative and Functional Medicine, 2nd ed, Richard S. Lord, J. Alexander Bralley, Metametrix Institute, Duluth, GA
4. The Detoxification Enzyme Systems, DeAnn J. Liska, PhD, Alternative Medicine Review, Vol 3, No. 3, 1998
5. Detoxification, Michael Murray, N.D., Joseph Pizzorno, N.D., The Encyclopedia of Natural Medicine, revised 2nd ed
6. Preventing Adverse Drug Reactions in Psychiatry, Pharmacokinetics:Substrates, Inhibitors, and Inducers of CYP 450, cytochrome p450 table, psychresidentonline.com
