The Low-Down on Fermented Tea, Part II: Metabolism & Detoxification

We have been in Japan now for 2 months, and it has been nearly that long since we have consumed any kombucha! In a land so important in the history of this fermented drink - not to mention one where fermented foods are ubiquitous and tantamount to a bowl of rice - I expected to find kombucha with relative ease. This however was not to be the case; even in the largest sprawling metropolitan area in the world.

Healthy Tea or Naive Abstraction?

My previous post, The Low-Down on Fermented Tea, Part I: The Microbiology & Chemistry, discussed the history of fermented tea, and how it is produced. With a brief hiatus from drinking kombucha, perhaps now is a good time to contemplate its potential health benefits and whether or not it should be a staple in one’s diet. As most readers surely know, there are many supposed health benefits surrounding kombucha, namely: improved metabolism and detoxifying effects, high levels of B vitamins, high levels of antioxidants (primarily polyphenols) and many in-quantifiable superpowers (i.e. clarity of mind, increased energy, etc.) which, if true, are likely a result of the aforementioned chemical attributes of the kombucha acting in a synergistic manner. On this note, we will try and keep this discussion somewhat scientific.

Any possible health benefits arising from kombucha consumptions are entirely based upon two mutually exclusive factors. Ultimately, the quality of the kombucha itself - primarily in terms of the levels and physico-chemistry (e.g. pKa, ionization state, chirality, polarity) of certain compounds (e.g. glucuronic acid, enzyme inhibitors/inducers); being mainly determined by fermentation parameters, tea selection and substrate choices. Penultimately, the drinks’ overall effect on the consumers' biochemistry; which is in and of itself highly individualistic (i.e. genetics/polymorphisms¹, diet, age, sex, pathological state, etc.). The primary objective with this post is to demonstrate that not all kombucha is created equal, nor is ones response to drinking said beverage. First, we will briefly outline metabolism and excretion and how they relate to detoxification. Specifically, the role that certain substances, such as glucuronic acid (GA), play in these processes and how this relates to kombucha.

Detoxification

The term "detoxification" typically refers to the removal of xenobiotics (substance not naturally produced or expected to be found within an organism - mostly the result of eating, drinking, breathing, etc.) from the body. The removal of xenobiotics is desirable because if the body cannot expel them, it will find a way to store them; typically in fat, as they are often lipophilic (fat soluble), or other tissues, depending on their polar nature. This bio-accumulation can lead to all sorts of complications, and diseases, and is "toxic" to the body, as the name implies (see Xenobiotic Flow Diagram). Basically, anything the body doesn't need to - or can’t - use should be expelled from the body and it’s bad news when this is not done with enough efficiency. This concept underlies the “toxicity” of various substances.

In effect, every substance administered to the body is "toxic" at different levels and timing. This concept is fundamental to the study of toxicology; at the heart of which lies metabolism. In fact, when studying toxicology one will often encounter the initialism "ADME" - Administration Distribution Metabolism Excretion (see ADME Flow Diagram). We will not go into detail regarding administration or the bio-kinetics of distribution, but focus on metabolism and how it prepares for the excretion phase.

An introduction to the study of ADME will accomplish two things: lay the foundational theory as to the mechanism of action for the main potential health benefit of consuming kombucha (elevating levels of glucuronic acid to aid in metabolism and excretion), while simultaneously demonstrating how we must consider each individuals response to drinking kombucha, and the necessity of optimizing the quality of the kombucha. In other words, ensuring that GA levels in the drink are actually high enough to elicit a notable increase in hepatic GA levels in the consumer; such that metabolism of xenobiotics is actually affected.

Absorption & Distribution

Since kombucha is ingested orally, we will focus on how substances are absorbed in the gastro-intestinal tract (GIT). The GIT is comprised of the mouth, esophagus, stomach, and intestines; being lined by the epithelium. The epithelium, lined with epithelial cells, acts as a physical barrier and is involved in absorbing nutrients. The GIT takes in food, digests it, absorbs energy and nutrients, and excretes the remaining compounds as waste, in feces and urine. The process by which this occurs is very complex and requires a decent understanding of biochemical concepts.

Basically, substances can be absorbed directly in the stomach, the small intestine, or the large intestine. The location of absorption is dependent on many factors, as are the mechanisms of absorption (i.e. filtration, passive diffusion, active transport, facilitated diffusion, phago/pinocytocis). Most absorption mechanisms employed for exogenous molecules allow lipophilic, non-ionized, compounds to be absorbed along the entire length of the tract. This is where things get complicated, as many compounds are ionizable. That being said, pH levels plays an important role in absorption, and compounds will typically be absorbed when they are non-ionized at the pH of the particular site, and are lipid soluble (weak acids typically absorbed in the stomach, weak bases absorbed in the small intestine).

Passive diffusion, possibly the most important absorption mechanism for exogenous molecules, is governed by Fick’s Law and the pH partition theory. Once a compound has been absorbed into the blood supply, its presence will depend on several kinetic factors. Again, depending on the physico-chemical properties (i.e. lipophilicity, pH, etc.), the compound will be distributed to tissues and target organs in a similar manner as with absorption from the GIT – by crossing a biological barrier (this time the endothelial lining of the vascular system) - once being carried to said site via the vascular system. The concentration of the compound in the plasma will give an indication of amount absorbed and the half-life of the substance in the body – a marker for the efficiency with witch metabolism and excretion are occurring.

Metabolism & Excretion

As mentioned, foreign compounds absorbed into biological systems often occurs via passive diffusion. This implies that the compounds are typically lipid soluble, in order to pass through the phospholipid bilayer of the lining cells of the absorption site (e.g. epithelial cells lining the GIT). Excretion from the GIT typically occurs via urine, faeces, or both (both of which are water based). Consequently, these lipophilic compounds are not suited for excretion. Therefore, the products of metabolism aim to be more water soluble (increase polarity) than the original compound, and thus more readily excreted. This will manifest in a reduced half-life, reducing the chance for toxicity.

Overview of Metabolism (Biotransformation):

Metabolism employs the use of several enzyme families, located at various sites throughout the body; such as the GIT and the liver. Metabolism is divided into two separate phases (see Metabolism Overview).

1. Transformation of a molecule into a more polar (hydrophilic) “metabolite” with the aid of enzymes and conjugates

2. Increase molecules weight and size to facilitate in excretion and elimination of compound from the organism

Phase 1 Metabolism

Thank you for reading this far, it's about to get good. As you can see from the above convenient diagram, metabolism can occur through two subsequent phases (Phase 1 and Phase 2), or solely through a single phase (Phase 2). In either case Phase 2 must occur -Phase 2 is important! This is where kombucha’s main potential health benefit arises².

Phase 1 metabolism is characterized by the alteration of the exogenous compound via the introduction of a new chemical reactive group, or the unmasking of an existing chemical reactive group, with the employ of biotransformation enzymes. Regardless of which alteration occurs, it will occur via either oxidation (cytochrome P450 enzyme family² & their isoenzymes), reduction (reductases – endogenous or from gut bacteria), hydrolysis (esterases & amidases), or hydration (hydrolases).

Phase 2 Metabolism

Phase 2 metabolism sees the enhancement for excretion of Phase 1 metabolites, or xenobiotics, already possessing a suitable reactive functional group, through conjugation reactions (covalent bonding) with endogenous hydrophilic compounds (e.g. GA); usually onto the reactive group introduced, or unveiled, in Phase 1³. This process promotes excretion and reduces toxicity by increasing water solubility of the xenobiotic. These conjugation reactions are carried out with the aid of transferase enzymes.

Phase 2 conjugation reactions are categorized by the type of endogenous hydrophilic compound used in said reaction. I will focus on those involving GA (glucuronidation), however they include also: sulphonation, glutathione conjugation, amino acid conjugation, acylation, and methylation. I am going to focus on glucuronidation, as it is one of the more important routes and it is that which is more pertinent to the discussion involving kombucha. Glucuronidation refers to the addition of glucuronic acid (which is hydrophilic) to a reactive group on another compound – typically a hydroxyl, carboxylic, amino, or thiol group – via glucuronosyltransferase; a reaction which will be discussed in more detail in the next post, “The Low-Down on Fermented Tea, Part III”. The degree to which this reaction is carried out depends, among other things, on the levels of GA in the GIT and hepatic system.

Assuming GA levels to be the limiting factor, if levels of a certain xenobiotic become so high so as to exhaust the GA supply, then those xenobiotics having undergone Phase 1 metabolism will be stuck in their reactive Phase 1 metabolite phase, as will those which already possess a reactive functional group and forgo Phase 1 transformations. This is clearly a problem and can lead to the dreaded bio-accumulation to which we previously eluded. In fact, the toxic effects are compounded by another phenomena – metabolic activation; whereby the transformation in Phase 1 elicits a toxic effect by forming a reactive metabolite (see Metabolism Flow Diagram).

As an example for metabolic activation, as well at glucuronidation, we can discuss the metabolism of Paracetamol (an analogue analgesic to acetaminophen, or Tylenol®, for the North Americans). When paracetamol is consumed at therapeutic levels, it is metabolized directly via Phase 2 glucuronidation with GA attaching to a thiol group, catalyze by uridine diphosphate-glucuronotransferases (UGT). As endogenous stores of GA deplete, an alternate metabolic route is utilized. This alternate route includes a Phase 1 activation, involving CYP2E1, to form the metabolite N-acetyl-p-benzoquinone imine (NAPQI)⁴. NAPQI is reactive and covalently binds to proteins necessary for regular cell function. This can ultimately lead to necrosis in the liver. This is normally not an issue, as NAPQI undergoes Phase 2 metabolism via glutathione conjugation. However, if enough paracetamol is consumed, the endogenous glutathione becomes exhausted as well, just as with the GA. Therefore the result of over consuming paracetamol is the buildup of reactive metabolite NAPQI (see Paracetamol Metabolism). This is just an example of how crucial Phase 2 metabolism is and how important diet can be in its regulation. By increasing the levels of endogenous compounds such as GA, by obtaining it exogenously, it can be possible to prevent, or reduce, the impact associated with the staling of Phase 2 metabolism. In theory, consuming a beverage with relatively high levels of GA might then accomplish such a feat? There are many more important questions to ask before drawing such a conclusion.

The Effect of the Consumers’ Biochemistry & the Individual Nature of Detoxification

Now that we have discussed how metabolism works, and how kombucha might help, we should discuss the other factor to consider when judging the aforementioned drinks effect on detoxification. Namely, how the individual responds on a biochemical level to its consumption.

Lets assume, for the sake of simplicity, that the kombucha which is being consumed has been nearly perfectly fermented, leads to an optimal pH in your GIT, has negligible anti-nutrients and crucial enzyme inhibitors, and has very high levels of biologically active GA (which we will discuss in The Low-Down on Fermented Tea, Part III). Furthermore, lets assume that it is consumed in a sufficient quantity and in a timely enough manner so as to raise the levels of endogenous GA significantly, with an adequate half-life so as to correspond with meal time (or the processing of exogenous compounds). These are all drastic assumptions to make when pulling a bottle off the shelf, forking over your hard earned dollars, and blindly putting your trust in some stranger that fermented tea for you. However, for arguments sake lets make these enormous assumption anyways, for now.

Individual Responses

Recall, we saw that Phase 2 metabolism is crucial and that it is here where kombucha shows the most promise? Well that whole process is regulated by the function of not only an enzyme, but a family of enzymes. As any good brewer knows, enzymes are temperamental. They need conditions to be just right in order to function .Okay, so again, lets make a big leap and say that conditions are ideal for the correct enzymes to function and that the food you ate with the kombucha didn’t affect any parameters governing the necessary enzymatic function. Even so, the presence, as well as the function, of these enzymes are all dependent on genetics. Specifically, the genes regulating expression and activity of the family of enzymes used for Phase 2 metabolism (CYP 1-4) are known to contain genetic polymorphisms which affect metabolism, and is a large reason for the variance in metabolism between individuals³.

An example of an analogous polymorph, is in a certain population of Asians, and involves their reduced ability to metabolize ethanol⁵.

A significant portion of this populations possess a polymorphism such that the rate of activity of alcohol dehydrogenase (ADH), the enzyme responsible for alcohol metabolism, is much higher. ADH is an enzyme family used in Phase 1 metabolism of ethanol, whereby acetaldehyde is created as a reactive metabolite, capable of being toxic and inducing liver damage ⁶.

Typical metabolic function would see acetaldehyde conjugated in Phase 2, for excretion. However, with the increased activity associated with having the ADH1B*2 allele, acetaldehyde is produced too fast and is therefore allowed to accumulate. Typical liver damage from over drinking is actually a compounding effect involving many factors, such as the leaking of lipopolysaccharides from the cell walls of Gram negative bacteria lining the GIT ⁷.

Another pertinent example of individual response lies in the sexes (e.g. some excretion pathways are favored over others). Females tend to eliminate glucuronidation conjugates via urine. In males, glucuronidation conjugates are excreted by hepatocytes from the liver, in bile, into the bile duct, into the intestine, and eventually eliminated as feces. The glucuronidation conjugates can then be broken down in the intestine by gut bacteria, and re-absorbed into the liver. If levels of the conjugate become too high, the active transport mechanism becomes saturated. This can lead to an accumulation in the liver which, depending on the compound, can result in hepatic tumors (liver cancer).

A Summary

This post was perhaps very dense and technical. In reality, this was really only a skimming of the surface. We wanted to introduce as many topics as possible regarding toxicology, as so many of its concepts should be of daily interest to us all. Regardless of your thoughts on how much diet actually affects our physiology and well being, or the role genetics play, individual food choices affect all of us through socio-economic and environmental concerns. Choosing food is harder now than it has ever been and we should always try and be cognizant of what we are eating; if not for ourselves then for those around us.

This post laid the foundation for examining the potential health benefits of drinking kombucha while introducing one of the most enticing effects – increasing endogenous levels of glucuronic acid. The post also investigated the complex biological response to the intake of foreign substances and the fallacy of a reductionist approach to making health claims. There is still plenty more to discuss in regards to health benefits, however in the next post we will discuss GA more in depth and look at ways to improve fermentation so as to produce it at higher levels.

References

Weber WW (1999) Populations and genetic polymorphisms. Mol Diagn4: 299-3072.
Guengerich FP (2008) Cytochrome p450 and chemical toxicology. Chem Res Toxicol21(1):70-83.3.
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Eng M, Luczak S, Wall T (2007)ALDH2, ADH1B, and ADH1C Genotypes in Asians: A Literature Review. Alcohol Res Health30(1): 22-276.
Edenburg H (2007) The Genetics of Alcohol Metabolism: Role of Alcohol Dehydrogenase and Aldehyde Dehydrogenase Variants. Alcohol Res Health30(1): 5-117.
Wang X, Quinn PJ (2010) Endotoxins: lipopolysaccharides of gram-negative bacteria. Subcell Biochem53: 3-25