The involvement of free-radical reactions in the development of many degenerative diseases has been repeatedly documented by researchers across the world. What may not be so widely understood, especially in the popular press, is the involvement of the oxidation-reduction potential in these disease processes.
The oxidation-reduction potential (redox potential) refers to the energy that a substance (or environment) has in relation to other substances (or environments) in terms of electron affinity. A substance with a powerful affinity for electrons is called an oxidizing agent. One that actively donates electrons (a substance with low affinity) is a reducing agent. Substances or environments that are electron-poor, we call oxidized. Electron-rich substances or environments are called reduced.
In terms of common chemicals, hydrogen is the prototypical reducing agent and hydrogen-rich chemicals are reduced. Oxygen is the prototypical oxidizing agent, and oxygen-rich substances are oxidized. As an illustration of the redox continuum, hydrogen-rich ethane (natural gas) can become progressively oxidized to ethanol (alcohol), acetaldehyde, acetic acid, glycolic acid, glyoxylic acid, oxalic acid, and finally to oxygen-rich carbon dioxide (see illustration).
When strong oxidizing agents are mixed with strong reducing agents, energetic reactions (like explosions) commonly result. Gunpowder is made from potassium nitrate (the oxidizer) and powdered charcoal (the reducing agent), with sulfur as a catalyst. Internal combustion engines are powered by gasoline (the reducing agent) and atmospheric oxygen (the oxidizer), with an electric spark to trigger the explosion at the proper moment to make the engine run.
In biological systems, carbohydrate and fat fuels are burned (oxidized) to generate energy. Ultimately, all of the energy needed to fuel the myriad of life processes comes from the energy of redox reactions.
Human bodies, and all other living organisms, are reduced relative to the atmosphere in which we live (see JMS #6 for an article on the reduced primordial atmosphere). The large energy difference between the reduced “chemicals of life” and the oxidizing atmosphere provide many times more chemical energy than that available without oxygen (i.e., through anaerobic metabolism). But the cost of maintaining the cellular environment in a reduced state requires substantial energy. What happens when this maintenance becomes impaired? What happens when the need for reducing power exceeds the available supply? What happens when the body starts to become oxidized?
During traumatic injuries which expose body tissues to atmospheric oxygen (scrapes, cuts, burns), a cascade of reactions are triggered in polyunsaturated fatty acids (PUFAs) present in cellular membranes which produce hormones called prostaglandins. These hormones orchestrate the defensive reactions to the injury — the initial vascular constriction to minimizing bleeding, the subsequent augmentation of blood flow to the injured area, the stimulation of cellular and humoral immune reactions, increased cellular replication and repair, and induction of fever. Once repair is accomplished, the redox potential returns to its normal reduced state and the defensive reaction abates.
The activation of immune function by oxidizing conditions may be a generalized function. Immune cells secrete reactive oxygen species (oxidizing free radicals) when stimulated by their target antigens. This function creates localized oxidizing conditions just as exposure to atmospheric oxygen does.
Oxidation may even play a role in antibody sensitivity to antigen. This hypothesis, first advanced by physician Robert Cathcart, suggests that antibody conformation (shape) is influenced by redox potential. The Cathcart theory hypothesizes that under oxidizing conditions, the disulfide (sulfur-sulfur) bridges between the two halves of the antibody is in its oxidized, intact, and active conformation, and that under reducing conditions, one (or more) of the disulfide bridges may become broken by becoming temporarily reduced to the sulfhydryl form. Hypothetically, this could alter the antibody conformation and temporarily inactivate the antibody complex.
If the Cathcart hypothesis is correct, the oxidation (redox) gradient in body tissues is a significant factor in immune activation, and impaired ability to maintain reduced conditions may lead to chronic immune hyper-activation and autoimmune disease.
The energy which maintains reduced conditions in animals is produced in two forms: 1) high-energy phosphate bonds (ATP), which can be hydrolyzed to donate energy to metabolic reactions, and 2) reduced hydrogen carriers (NADH, NADPH, and FADH2), which can either be used directly as a chemical reducing agent or be converted into high-energy phosphate bonds.
The reduced redox potential in tissues is largely determined by the dominance of certain key reducing chemicals: ascorbate (vitamin C), and reduced thiols (especially glutathione). These reduced chemicals become temporarily oxidized when they interact with oxidizing agents and oxidizing free radicals, but they then become re-reduced to their active forms by the body's primary reducing chemicals: the hydrogen-carrying NADH, NADPH, and FADH2.
Even with ample reducing power available in healthy cells, small amounts of oxidized ascorbate and glutathione are constantly being produced by stray free radicals produced by endogenous metabolism (e.g., mitochondrial energy production) or exogenous factors (e.g., ionizing radiation). But when available reducing power falls or oxidative stress peaks, the percentage of oxidized ascorbate or glutathione can rise to levels which can impair health or threaten life.
The ascorbate-dehydroascorbate redox pair is one of the most important factors in the maintenance of reduced conditions. Ascorbate is used to reduce other antioxidants (vitamin E, glutathione, etc.) that have become oxidized. In this process, ascorbate is oxidized to dehydroascorbate (DHA), which is then reduced back to ascorbate by NADH, NADPH, FADH2.
In the illustration below, redox potential is graphed versus
the ascorbate-dehydroascorbate ratio. Under reduced conditions
(top of graph), most of the ascorbate is reduced. As conditions
become more oxidized (moving downward on the magenta “S”
curve), the percentage of ascorbate begins to fall off more and
more rapidly, passing through 50% and then slowing down as the
concentration of ascorbate approaches zero.
In biological systems, the redox potential must be kept reduced at all times to perpetuate the life process. In other words, the concentration of DHA must be kept to a minimum. Under oxidizing stress (injury or disease) or impaired ability to manufacture NADH (aging or disease), the concentration of DHA can rise as the redox potential slips. This is a potentially life-threatening state (which may be the event which triggers sudden infant death syndrome).
The initial rate at which the redox potential falls as DHA increase is initially slow — on the “top shelf” of the curve. But as DHA increases further, the redox potential falls faster, becoming progressively more antagonistic to the metabolic processes of life. Ultimately, if the process is not stopped, the organism “falls off the shelf” and slides down the cliff into death.
Supplemental ascorbate is an immediate remedy to this catastrophe. Each ascorbate molecule carries two hydrogen atoms (and two electrons) which would otherwise have to be supplied from cellular metabolism. This shifts the ascorbate/DHA ratio towards ascorbate and raises the redox potential back onto the shelf.
The central role of reducing power in the recycling of antioxidants and free radical scavengers suggests that reducing power is frequently the limiting factor in response to oxidant stress. The total reducing equivalents carried by all of the non-enzymatic antioxidants is small compared to the amount carried over their lifetime in the body. It is their rapid recycling that accounts for their effectiveness.
Using Dr. Cathcart's analogy, the antioxidant defense system is like a bucket-brigade fire department. Just as the fire is extinquished by the water carried by the buckets, oxidizing stress is quenched by the reducing power carried by antioxidants. If a bucket brigade used each bucket only once, they would be dramatically impaired in their ability to put out fires. Likewise with antioxidants, if they were not continuously recycled, they would be quickly consumed by free radical stress.
Ascorbate is an ideal carrier of reducing power. It's toxicity is extremely low, and it can be taken orally in multiple-gram amounts or infused directly in hundreds-of-grams-per-day amounts. Ascorbate is assimilated extremely rapidly and actively “couples” with oxidized sulfur compounds returning them to their reduced sulfhydryl forms. It is the only substance known to meet all these criteria.
The use of ascorbate to provide reducing power is analogous to giving our bucket-brigade fire department a huge number of pre-filled buckets. It doesn't matter so much if the used buckets don't get efficiently re-filled when there are huge numbers of filled buckets available for the emergency. Intravenous vitamin C is like giving the fire department a 3-inch hose hooked up to a fire hydrant.
Supplemental ascorbate has been used by Dr. Archie Kalokerinos to prevent immunization-induced sudden infant death syndrome (SIDS) in Australian aborigines (see Every Second Child). Dr. Klenner and Dr. Cathcart have used ascorbate supplements to treat viral and bacterial diseases. Dr. Cathcart has used intravenous ascorbate to reduce morbidity from infectious diseases and to arrest certain autoimmune diseases. Dr. Linus Pauling uses oral vitamin C to prevent the common cold and other infectious diseases.
Although ascorbate is an ideal carrier of reducing power, the most active of the dominant reducing agents are sulfhydryl (sulfur-hydrogen) compounds (see illustration below). Sulfhydryl compounds can donate hydrogen atoms to other chemical reactions fairly easily because the large outer electron shell “delocalizes” the odd remaining electron and minimizes its energy state. These sulfhydryl radicals tend to be relatively stable in comparison to other free radicals, and preferentially dimerize into disulfides which are of low toxicity. Disulfides can then be reduced (unoxidized) back into their sulfhydryl forms. This recycling system functions well as long as adequate reducing power is available.
Glutathione (G-SH) is the predominant sulfhydryl reducing agent in animals. G-SH (gamma-glutamylcysteinylglycine) is a tripeptide of the amino acids glycine, glutamine and the sulfhydryl-containing cysteine. It participates in redox reactions throughout the body, including the reduction of DHA to ascorbate.
While reduced sulfhydryl bonds play a vital role in antioxidant defense, oxidized disulfide bonds are critical determinants of the three-dimensional structures of proteins and enzymes throughout the body. Proteins are initially produced as linear polymers of amino acids, some of which contain sulfhydryl groups. These polymers fold and spiral into 3-D structures which can become bridged with sulfur-amino-acid-to-sulfur-amino-acid bonds. These sulfur-sulfur bonds lock the protein and enzyme into a stable configuration which is essential for its function. When these bonds break (by free radical hydrolysis, for example), the protein or enzyme can come loose or unravel.
Most sulfur-sulfur bridges in enzymes and proteins are protected from such potential damage by being buried inside the folded 3-D structure. Some sulfur-sulfur bridges, however, are exposed. In the case of antibodies, this may actually be by design.
Antibodies are manufactured from four polypeptide chains which are joined by disulfide bridges. There are two identical long chains joined by two disulfide bridges, and two identical short chains that are attached to the long chains by one disulfide bridge each (see illustration at right). Antibodies work by the affinity of the four variable regions of the antibody (the shaded areas in the illustration) for the antigen. If both parts stick, the antibody attaches. If only one or none does, the antibody doesn’t attach to the antigen.
The sulfhydryl groups attaching the various chains on the antibodies may be redox sensitive. Although such an effect has not yet been documented, severe autoimmune reactions do appear to be quenched by massive ascorbate infusions [Cathcart, personal communication]. Such redox sensitivity would establish a localization phenomenon for antibodies that would parallel that already documented for prostaglandins.
Focussed antibody activity may provide a selective survival advantage over diffused antibody activity. Localization may augment the intensity of the immune response and simultaneously decrease the likelihood of unwanted autoimmune reactions.
The redox-sensitivity hypothesis offers some interesting speculations regarding the influence of aging on immune competence. With aging, redox potential slowly becomes more oxidized. This may be responsible for systemic activation of antibodies and the increased likelihood of autoimmune disease associated with aging. It also would be predicted to diminishes the strength of the antibody attack on a localized antigen because of dilution and an increase in the oxidative diffusion from the local infection site (see sidebar).
For acute autoimmune disease, intravenous ascorbate is required to quickly restore a reduced body state. Dr. Cathcart uses 100-200 grams over 24 hours to shut down the hyper-reactivity of antibodies. Once stabilized, patients are instructed to maintain oral ascorbate at 90% of their bowel tolerance dose (the dose that would cause diarrhea). In some patients, this is adequate to control symptoms. In others, there are occasional episodes or exacerbations of symptoms that may require an intravenous infusion.
The most significant drawback to this protocol is patient compliance. Staying within 10% of the bowel-tolerance dose is difficult and requires constant readjustments of dosage. Bowel tolerance doses fluctuate with state of health, and are therefore not static. During episodes of infection, the bowel-tolerance dose can increase several-fold within hours. This kind of instability requires constant upwards adjustments of vitamin C intake which always carry the risk of loose bowels (diarrhea). Although Cathcart’s most dedicated patients have been able to follow his protocol for years, patients for whom this is not a life-and-death matter are often less than enthusiastic about flirting with diarrhea as a lifestyle risk.