LINUS PAULING INSTITUTE RESEARCH REPORT
An Interview with Tory M. Hagen,
Q: In your work on the biochemical and metabolic problems that develop as animals age, you've identified critical substances that you call "age-essential." What are age-essential micronutrients?
A: As individuals age, there is a greater need for certain substances that may be present in the body or in the diet in sufficient amounts when we're young. We have found two compounds that we call age-essential micronutrients. One is carnitine, which is an amino acid derivative of lysine normally synthesized in our livers. We found that the synthetic capacity for carnitine declines dramatically with age, so that an elderly individual makes only about half as much as a younger individual. This is a very important problem because carnitine is involved in energy production and metabolism, so its loss contributes significantly to the decline in energy that many elderly people experience. Carnitine is a critical micronutrient that elderly people need in larger amounts.
Lipoic acid, which is a derivative of a fatty acid, octanoic acid, is another age-essential micronutrient. It's simply a carbon compound with two thiol, or sulfur containing, groups that is made in our bodies in the mitochondria, which are organelles in the cell that produce energy. Like carnitine, lipoic acid is normally used as a cofactor to convert raw dietary fuels into usable forms of energy for the body to carry out metabolic processes. Dihydrolipoic acid is the reduced form of this compound; lipoic acid is the oxidized form. Together, they form a redox couple and can accept and give off electrons. They can also accept and donate chemical groups, which is a useful property in energy metabolism in the body.
Q: If dihydrolipoic acid functions as the antioxidant, why do you give lipoic acid instead to animals in your experiments?
A: Dihydrolipoic acid is less stable and auto-oxidizes in air. Like butter, it will become rancid if left out too long. So if we give lipoic acid to animals, which is the oxidized but stable form, it is taken up by the body. Cells can reduce it to the dihydro form, which then functions as an antioxidant.
Q: Are commercially available lipoic acid supplements identical to the substance that you use experimentally?
A: There are slight differences. The commercially available forms are made synthetically, which results in a mixture of molecules that have different chirality, or "handedness." In spatial orientation, if you were to look at the molecular structure like Dr. Pauling would have, there is a left-handed form and a right-handed form of the molecule. The commercially available lipoic acid is a mixture of right-handed and left-handed forms, about 50% of each, although both forms have exactly the same chemical composition. This mixture of different forms is called a racemic mixture.
When we make lipoic acid in our body we make the right-handed or R form of the molecule, which is the one that the body utilizes. The R form is used biologically in energy production from raw fuel sources. The left-handed or S form of the molecule seems to be much less able to be reduced to the very powerful antioxidant form. It also doesn't seem to be absorbed in the body in the same way. If you take a commercial supplement of lipoic acid, you may not be getting as much usable lipoic acid into the body as you would with the natural form of the molecule.
Some studies have found no difference between the R and the S form in antioxidant potency once it was reduced. But there is also experimental evidence that the S form was not able to protect cells to the same degree as the R form, especially in cataract formation. In our studies that compared the S and R forms, we found the R form to be more potent in protecting cells in experimental conditions. We found the racemic mixture to be less potent but still beneficial, and we found the S form to have no benefit at all under the particular experimental conditions.
Q: Vitamin C is considered to be the most powerful antioxidant in plasma. How do the antioxidant functions of lipoic acid differ from those of vitamin C, and what other biochemical effects might lipoic acid have that aren't found with vitamin C?
A: Vitamin C is indeed a very potent antioxidant. While we know quite a lot about vitamin C, we still have much to learn about its biological functions. Lipoic acid is actually a more powerful antioxidant than vitamin C on the basis of its redox activity—the ability to donate or accept electrons. In plasma, vitamin C is maintained at relatively high concentrations. Ingested lipoic acid will spike in the plasma very quickly and then be removed because it's being taken up by cells. So you do not see a sustained level of lipoic acid in plasma after an oral dose. On the other hand, vitamin C remains in the plasma for much longer after ingestion. Chemically, lipoic acid may be more powerful but biologically vitamin C is far more effective as a long-term antioxidant. But this tells us that lipoic acid may have other special functions. We have found that the age-related decline in tissue vitamin C levels in elderly animals can be reversed by giving them lipoic acid. The age-related decline in glutathione, a cellular antioxidant, can also be reversed by feeding old rats lipoic acid. Even though lipoic acid is transient, it seems to have some dramatic effects. We are starting to define these mechanisms—why lipoic acid has such a potent effect on other antioxidants and therefore boosts overall the antioxidant capacity that otherwise declines with age.
Q: Is lipoic acid actively transported into cells like vitamin C?
A: Vitamin C is taken up in cells by two mechanisms. In its oxidized state, called dehydroascorbic acid, it piggybacks onto the glucose transport mechanisms of the cell and then is reduced in the cell to ascorbic acid, a potent antioxidant. Ascorbic acid can also be taken up by many cells using the sodium-dependent vitamin C transporter, which is a special membrane protein. Lipoic acid is very similar. It appears to be actively taken up by the cell's general vitamin transport mechanisms. There is also some evidence that lipoic acid may act like its precursor, a fatty acid, and transverse the cell membrane.
Q: Do you think that lower vitamin C levels in the elderly, caused by less efficient transport or diet, have much of an impact on health?
A: It is very clear that the general health of the elderly correlates with vitamin C status, although many factors are involved. Institutionalized or hospitalized elderly people generally have very poor health and diets, and their vitamin C status is impaired. Why do we see this loss in vitamin C status? It could be due to poor absorption from the diet, less effective cellular uptake, or it could be caused by a greater utilization of vitamin C because of the enhanced oxidative environment in older people. We have used old rats to study these issues.
Q: How old is an elderly rat?
A: An old rat is between 24 and 28 months of age, which is about equivalent to a 75- or 80-year-old human.
Q: So these rats are near the end of their life span?
A: Yes, and we compare them to younger animals. We always do these comparative experiments to discern differences in mechanisms. A very bright student in my laboratory, Alex Michels, has focused on these experiments. We looked at the uptake of vitamin C into tissues and found that the transporters responsible for vitamin C uptake are defective in old rats, tending to decline in their overall activity. Alex found that the transporters are still present in the cell, but they are made in smaller amounts. In other words, the gene is not creating the protein at the same level as in young rats. Also, the protein itself is abnormal. Its conformation has been altered so that the amount of vitamin C needs to be increased in order to achieve good uptake by cells.
Q: Is this an example of a molecular disease?
A: In some ways, yes. We can somewhat overcome this "sick protein" by increasing the amount of vitamin C, which results in better transport. Subsequently, vitamin C levels are replenished, which leads to lower oxidative stress in these old rats.
Q: Is it also possible to increase the cellular concentration of vitamin C in the old animals by giving lipoic acid?
A: Yes. In this case, it appears that lipoic acid is not acting as an antioxidant but instead is acting as a signaling molecule to induce more cellular uptake of vitamin C. You can overcome the sick transport protein by giving more vitamin C, or you can administer lipoic acid to rejuvenate the amount of the protein and thereby allow more vitamin C to be taken up by cells.
Q: Your work has focused on age-related mitochondrial dysfunction in the heart and liver that affects energy metabolism and protects against oxidative stress and toxins. Your recent work investigated oxidative stress in the rat heart. What have you found?
A: Our strategy is to examine the response to age-essential micronutrients, carnitine and lipoic acid, both individually and in combination to see how mitochondrial function in the heart is affected. The heart is an amazingly active organ that must continue to beat throughout our lives, so it is full of mitochondria—50% of heart volume is actually mitochondria, which produce energy. That tells you how energetically active the heart is. But the heart, unlike other organs, cannot store energy to maintain its function. It has only about 4 minutes of energy reserves. Those reserves decline even more in the aging heart. That's why heart attacks in the elderly are even more lethal than in younger people. You simply cannot overcome the stress of the lack of energy, and the heart will die very rapidly. We think the heart is a very good model to study the role of mitochondrial dysfunction in aging. Mitochondria are the Achilles' heel in aging—our vulnerability to age-related problems is closely tied to mitochondrial function.
Q: Does the combination of carnitine and lipoic acid produce better results than either substance alone, and if so, why?
A: In some conditions, one compound seems to be very good for the apparent end point that we are studying, and in others we see a synergistic effect when we combine the two. We are using lipoic acid to find out if we can dramatically lower overall oxidative stress in the heart. If you lower oxidative stress, you decrease damage to the mitochondria. We have found that the mitochondria tend to function better with lipoic acid. Carnitine achieves the same result but in a different manner. With age, you lose the ability to burn fatty acids and create ATP, adenosine triphosphate, which is the energy currency in the body. Carnitine is involved in this process of converting fatty acids into a usable form of energy. We found that carnitine levels decline rather dramatically with age and that a protein that transports the fatty acids and carnitine into the mitochondria becomes dysfunctional. In aging animals and people, the heart becomes starved for its major fuel source, fats. If you give supplemental carnitine, you can improve the function of that sick protein, and fatty acids can then be taken into the mitochondria and utilized more efficiently. So, we find that lipoic acid and carnitine work very differently—they are working on different end points—but together they take care of the oxidative stress and the metabolic decline that occur with age, thereby allowing the heart to work much better for a longer period of time.
Q: You've given carnitine and lipoic acid to animals in their food. What have you learned about the dose-response relationship?
A: Our new grant from the NIH will help us to determine the optimal dose in these animals, namely, the effective dose that improves mitochondrial function and decreases oxidative stress. We don't want to give too much or too little. We do not know the appropriate dose for humans either, and we have to work this out in animals first. We want to find out if these age-essential micronutrients exhibit side effects or other problems at various doses. We haven't seen many problems even at very high dosages in rats, so we think that these compounds are very safe. We do know that if you give too much carnitine or lipoic acid to rats, the benefit diminishes. Right now, we are titrating the dose to find an optimum.
Q: Are you aware of any supplementation studies in humans with carnitine and lipoic acid that found a deleterious effect at any dose?
A: We have worked with scientists at San Francisco State University to examine the benefit of exercise in the elderly. We wanted to learn if the overall energy of the individual could be enhanced with lipoic acid and carnitine and in that study conducted a relatively small, placebo-controlled preliminary trial to see also if any deleterious effects occurred. We saw an improvement in overall exercise ability—in other words, more stamina—and we saw no untoward effects at the dose we used. That is the only trial that I know of where lipoic acid and carnitine have been combined. We also have a placebo-controlled trial under way at Boston University School of Medicine to look at this more rigorously and in greater detail. We haven't observed any side effects, but we have to wait to see if there is any statistically significant benefit for the population being studied. We are giving only a single dose of these substances, and we do not yet know if this is the optimal dose.
Q: You've published some work on feeding lipoic acid to beagles. Did you find any harmful effect of lipoic acid in that study?
A: None whatsoever. In fact, we found just the opposite. We saw dramatic improvements in their short-term memory, so lipoic acid has benefit not just to the heart but also to memory function. We've seen this in rats as well. Both old rats and old beagles supplemented with lipoic acid seem to have much better spatial orientation.
Q: What might explain the improvement in memory and cognitive performance in old animals supplemented with carnitine and/or lipoic acid?
A: Again, we think it involves the mitochondria. There is good evidence that the mitochondria in the brain, especially in certain parts of the brain, are very important in memory function because of their energy production and effects on oxidative stress and damage. Mitochondrial dysfunction is associated with many senile dementias, such as Alzheimer's disease, Parkinson's disease, and others. We think that carnitine and lipoic acid cross the blood brain barrier and would have benefit to the brain.
Q: Have there been any human clinical studies using carnitine and/or lipoic acid on the progression of Alzheimer's disease or other neurodegenerative diseases?
A: For lipoic acid, I'm not aware of any published trials with neurodegenerative disorders, except for multiple sclerosis. In animal models of multiple sclerosis, lipoic acid seems to be a very good means of maintaining remission. There is some similar anecdotal evidence in humans. Carnitine, in the form of acetyl-L-carnitine, has been found in clinical trials to delay the progression of Alzheimer's disease. It has been shown to be somewhat effective in the quartile of subjects that had the most rapidly progressing form of Alzheimer's. In the slower progressive form, there did not seem to be any great benefit, at least with the trials that have been published to date.
Q: Commercial supplements of carnitine are usually found as L-carnitine or acetyl-L-carnitine. What's the difference between these?
A: Carnitine is a derivative of lysine, an amino acid, and acetyl-L-carnitine has an acetyl group attached to carnitine. Acetylation of carnitine can arise naturally in the body through normal metabolic processes. The body can absorb carnitine, especially from meats, but the acetyl group increases absorption. Both forms are effective and eventually get into the body as carnitine, but the acetyl form seems to be a little bit better absorbed and distributed more universally within the body, whereas carnitine tends to end up in muscle tissue. In our animal studies, we've used acetyl-L-carnitine almost exclusively.
Q: Do you have any plans to conduct long-term feeding studies with these substances in young or middle aged rats to assess the metabolic or cognitive changes as they age?
A: These are extremely expensive experiments, but we are conducting some in collaboration with our colleagues at UC-Berkeley, especially Dr. Bruce Ames. We are engaged in long-term trials in which animals are dietarily supplemented with acetyl-L-carnitine and lipoic acid for at least one year. Our preliminary results show that the combination seemed to improve the animals' overall stamina. We have begun to assess the metabolic affects and should have some results soon.
Q: There has been some speculation that age-related iron accumulation in the brain may cause problems. How does lipoic acid affect this, and do you think that long-term supplementation with lipoic acid might help prevent iron accumulation in the brain?
A: We just completed a relevant study in our laboratory in collaboration with Dr. Balz Frei, which suggests that lipoic acid chelates, or binds to, iron and other metals very strongly. This has been known for some time, but our recent work shows that lipoic acid will bind free metal ions so that they cannot catalyze free radical production. Iron is a double-edged sword for the cell. On the one hand, we need it for metabolic processes. However, free iron that is not bound and tightly held in proteins can catalyze free radical reactions. It appears that we accumulate free iron and other metals that can catalyze free radical reactions as we age. The amount of iron in certain regions of the brain doubles or even increases four-fold with age. We have evidence that at least part of that accumulation consists of iron capable of catalyzing free radical production. We wanted to find out if lipoic acid could bind to metals in living organisms and looked at age-related iron accumulation in the rat brain as well as how that is affected by lipoic acid supplementation. We fed lipoic acid to old and young animals for two weeks and analyzed their overall iron and copper levels and oxidative stress parameters. We found a dramatic reversal in the age-related increase in iron and copper in the elderly rats. Remarkably, the iron levels in old rats actually decreased to levels seen in young animals, but didn't go lower than those normally observed in young animals. This suggests that lipoic acid is not removing iron from proteins that need it, but is simply eliminating excess iron. Improvements in cognitive function and oxidative stress parameters significantly correlated with the decline in iron levels. We were able to substantially lower levels of oxidative damage to DNA and proteins that correlated with this overall equilibration of iron levels in the aging rat brain.
Q: A large NIH grant that established LPI as a Center of Excellence for Research on Complementary and Alternative Medicine was recently awarded to you, Dr. Balz Frei, and Dr. Joe Beckman. What aspect of your research will this grant fund?
A: We are really excited about this program project grant. My project is related to what we have learned about the effect of age-essential micronutrients on the mitochondria. We will examine lipoic acid in much more detail. Lipoic acid is a bit of a conundrum. On the one hand, it is a very potent means of reversing the loss of antioxidants and stress response that protects animals against oxidative stress. Lipoic acid diminishes the age-related vulnerability to environmental and toxicological insult, which is a major hallmark of aging. On the other hand, lipoic acid from the diet simply doesn't stay in the body very long. Biologically, it is a very short-lived molecule. Plasma levels spike about 1-2 hours after taking it, but after about 4 hours you don't even find it in the plasma anymore. So it's taken up, used by the cells, and then released via the kidneys and excreted very rapidly. So how does lipoic acid cause these dramatic long-term effects, and how does that jibe with what we know about its pharmacokinetics? Our new grant will allow us to explore these issues. We think lipoic acid is not simply acting as an antioxidant, but also functions as a signaling molecule that initiates other biochemical events in the cell. In fact, we think lipoic acid may actually be a mild stressing agent—a substance that the cell wants to get rid of and therefore induces antioxidant and detoxification genes. This then causes an overall long-term increase in the cell's protective mechanisms. Since lipoic acid may affect as many as 300 genes involved in immune response, antioxidant and stress response, and toxicological response, it may have a global and sustained effect. We are really excited that this naturally occurring compound could allow us to boost our protection against a variety of insults that becomes impaired with age. We already are making progress in this aspect of gene-nutrient interaction and recently published a paper showing that lipoic acid is acting to induce gene expression. This is very exciting, especially concerning the elderly. With our colleagues, Drs. Fred Stevens and Claudia Maier, we also have begun to investigate the effect of lipoic acid on protein structure and function.
Q: Lipoic acid has been used to treat diabetic neuropathy for many years in Europe, apparently with some success. It has also been used to treat mushroom poisoning. Do you think that there might be a general role for lipoic acid in protecting us from many different toxins, such as mercury, lead, and other environmental contaminants?
A: Lipoic acid has been used to treat mercury poisoning. Its thiol nature allows it to bind to metals like mercury and remove them from the body. Lipoic acid does have potential and actual clinical use in removing heavy metals and other toxins. Again, two roles may be involved—chelating and removing heavy metals, and, more indirectly, upregulating detoxification genes and enzymes that help remove toxins from the body.
Q: Is there any reason to suspect that lipoic acid might also be useful in preventing an age-related degenerative problem like cancer?
A: I think that would be a very valuable line of research and needs to be further explored. Many of the detoxification genes activated by lipoic acid play a role in the prevention of cancer, so it is reasonable to speculate that lipoic acid may be useful in this area. We will continue to investigate the effect of lipoic acid on mitochondrial dysfunction and plan to examine its role in age-related diseases as well.
Q: Do you have any recommendation for lipoic acid or carnitine supplementation in people?
A: Unfortunately, we're not yet able to make specific recommendations for optimal health. We are working out the optimal dose in animals, which needs to be fully understood before accomplishing this in humans. Until we know potential side effects—even though we don't see any yet even at very high doses—I'll refrain from making recommendations.
updated May, 2004
Micronutrient Research for Optimum Health
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