The Goal: To Find Practical Methods of Retarding The Aging Process
By Richard Weindruch and Stephen R. Spindler
Vitamin E protects our membranes from oxidation damage. In fact, vitamin E is the major membrane antioxidant. It addition, it can break the self-perpetuating chain of oxidative reactions initiated by damage to unsaturated fatty acids in our membranes. Vitamin E also keeps selenium reduced chemically, which is important for selenium's antioxidant activity. It may also decrease cancer-causing nitrosamine formation in the stomach.
High blood levels of vitamin E in the diet, or from supplementation are associated with health and longevity (Diplock, 1994; Diplock, 1996). The populations of entire European countries with higher-than-average blood levels of vitamin E have lower mortality from coronary heart disease than populations with low vitamin E levels. This correlation is even stronger when corrected for the effects of blood cholesterol and smoking.
A prospective investigation of 39,910 male health professionals found that men with intakes of vitamin E of at least 100 to 400 IU per day were protected from coronary heart disease. No greater protection was found at higher dosages (Rimm et al., 1993). The Nurses' Health Study, which began in 1976, examined the dietary habits of more than 87,000 women (Stampfer et al., 1993). Women with a high dietary intake of Vitamin E (above 100 IU per day) showed a significant reduction in the risk of heart disease.
A study in Linxian County, China, suggests that vitamin E also may help prevent cancer. The people in and around Linxian have low intake of micronutrients, and one of the highest rates of esophageal and stomach cancer in the world. Supplementation with vitamins and minerals (one to two times the recommended daily allowance, or RDA) in 30,000 adults from 1985 to 1991 showed a significantly lower death rate, especially from cancer, in subjects receiving beta carotene, vitamin E and selenium. (Blot et al., 1993). Other case-control studies show some evidence that low serum concentrations of vitamin E and beta-carotene are risk factors for senile cataracts.
Finally, the results of placebo-controlled clinical trials conducted in elderly men and women indicate that vitamin E raises levels of vitamin E in the blood and increases immune system responsiveness. These data suggest that a part of the decline in immune function with age may be related to oxidative damage, which can be prevented by vitamin E supplementation.
Both humans and animals synthesize alpha lipoic acid, but we do so in only very small amounts. Most of our alpha lipoic acid is bound to an enzyme complex which functions in energy production inside our cells.
When the diet is supplemented with alpha lipoic acid, the serum and membrane levels of the antioxidant rise slowly, with relatively low toxicity. Alpha lipoic acid acts both in membranes and in the water-containing parts of the cell. It is fat-soluble like vitamin E, but is converted into a water-soluble form called dihydrolipoic acid. Both the membrane and water-soluble forms of the antioxidant accumulate in the body to work together as a very potent antioxidant (Stahl & Sies, 1996).
Alpha lipoic acid is especially effective in recycling other antioxidants, such as vitamin E, back to their original form after they detoxify free radicals. In the late 1950s alpha lipoic acid was found to prevent scurvy in Vitamin-C-deficient guinea pigs, and to prevent the symptoms of vitamin E deficiency in rats. This showed that small amounts of Vitamin-C and E had been preserved and regenerated in the deficient animals. There is normally only about one molecule of vitamin E per 1,000 to 2,000 phospholipid molecules in our membranes. But this small amount goes a long way because it is constantly regenerated by other antioxidants.
After vitamin E detoxifies a free radical, it becomes a free radical itself, but is quickly returned to its antioxidant form by interaction with other antioxidants like alpha lipoic acid. Alpha lipoic acid also increases the intracellular concentration of glutathione to maintain the proper level of oxidation-reduction potential for proteins inside cells.
Alpha lipoic acid detoxifies and chelates, or combines chemically with, transition-state metal ions like cadmium, copper, zinc, and possibly iron. Each of these metal ions can generate toxic oxygen radicals if they are freely present in cells or blood.
Alpha lipoic acid may be beneficial for diabetes (Stahl & Sies, 1996), which many gerontologists regard as a form of accelerated aging. Much of the damage in diabetes results from free-radical generation during a process known as glycation, which involves the binding of glucose with protein molecules. Alpha lipoic acid reduces glycation damage caused by blood glucose. It seems to make muscle and fat tissues more sensitive to insulin, which enables them to take more glucose from the blood, thus lowering blood glucose levels. Once inside cells, glucose is converted into compounds that produce little glycation damage. Because glycation leads to atherosclerosis, kidney disease and loss of vision, alpha lipoic acid may ameliorate these conditions.
Alpha lipoic acid seems to reduce the kind of damage that occurs during heart attack and stroke, although these results have been found only in animal models thus far. There also are a few reports that alpha lipoic acid may improve memory in experimental animals.
Coenzyme Q10 (CoQ10) is a small, vitamin like molecule which is an essential component of the electron transport chain in mitochondria, the power plants in our cells. ATP (adenosine-tri-phosphate) is the energy molecule used inside cells to do work. ATP is fabricated in mitochondria. The electron transport chain is the biochemical pathway by which electrons extracted from food are used to fabricate ATP. In the process, the electrons convert the oxygen in air to water. CoQ10 is an electron acceptor and donor. It shuttles electrons back and forth between several of the enzymes which carry out ATP fabrication.
In addition to its function as an electron shuttle, CoQ10 is an antioxidant (Beyer, 1992; Kanter, 1994), which may be especially important inside mitochondria. The electron transport chain generates about 1 trillion oxygen radicals per cell every day. About 2 percent of them get free of the enzymes that try to hold on to them until they can be used to generate energy. These free oxygen radicals are very dangerous to the mitochondria, but also to the rest of the cell. In fact, the reason electron transport takes place in membrane-bound sacks such as mitochondria is, in part, to keep these free radicals trapped inside the mitochondria. This is why having a strong antioxidant like CoQ10 in mitochondrial membranes is important.
Supplementation with CoQ10 raises the levels of this antioxidant in our cells and tissues. Furthermore, CoQ10 increases the activity of the electron transport chain, improving energy generation by mitochondria. We gradually lose some of our ability to produce energy from the food we eat as we age. Supplementation with CoQ10 partially reverses this loss, especially in the heart muscle. In animal experiments, CoQ10 protected the heart against oxidative damage caused by the blockage and restoration of blood flow (Mortensen, 1993). In animal studies, CoQ10 protected the brain from oxidative damage (Beal et al., 1994) and protected the liver from free-radical-generating toxins.
Many tissues use a metabolic strategy termed beta oxidation to "burn" fatty acids to obtain energy. This activity takes place in the mitochondria. Carnitine is a small molecule resembling an amino acid. It serves as a sort of ticket or tag for entry into the mitochondria. Carnitine is chemically attached to the fatty acids in the cell cytoplasm outside the mitochondria. A transport system in the mitochondrial membrane recognizes the attached carnitine ticket, grabs it along with the fatty acid, and moves them both into the mitochondria. Once inside, carnitine is removed from the fatty acid and transported back outside the mitochondria so it can be used again.
In heart mitochondria, this transport process decreases with age, as does mitochondrial function. A decrease with age also has been found in the body's pool of carnitine. This decrease may be responsible for some of the age-related loss in mitochondrial function. There is a growing body of scientific evidence indicating that the accumulation of mitochondrial defects with age can be slowed or reversed by supplementation with acetyl-L-carnitine (ALC) (reviewed in Shigenaga et al., 1994). ALC is the natural precursor to both carnitine and acetylcholine (a "neural transmitter").
Acetyl-L-carnitine improves mitochondrial function in several ways (Shigenaga et al., 1994). For example, ALC fed to old rats increases mitochondrial cardiolipin levels to those of young rats. Cardiolipin is a natural component of mitochondrial membranes, that is important for membrane structure and function. It also is important for the functioning of the enzymes responsible for energy generation within the mitochondria. Aging decreases the cardiolipin content of mitochondria in heart, liver and brain, which generates extra oxygen radicals.
ALC helps to reduce oxidative damage with age, and protects the brains of experimental animals from age- and stroke-related neural degeneration. In humans, one controlled clinical trial showed that the progression of Alzheimer's disease was significantly reduced in patients receiving 2 grams per day of ALC for a year (Bowman, 1992). We will conduct the first test of the effect of ALC supplementation on lifespan.
Cysteine is a non-essential amino acid used for protein synthesis. Although we make some cysteine in our cells, it is also the rate-limiting amino acid for the synthesis of glutathione, a small molecule that plays many essential roles in cells. Cysteine is unstable, somewhat toxic, and weakly mutagenic when taken orally or by injection. But procysteine, a modified form of cysteine, is somewhat less toxic, and much more stable "on the shelf" than cysteine (White et al., 1993). It is rapidly converted into cysteine and carbon dioxide inside cells. This conversion makes it good for raising intracellular concentra- tions of cysteine, which, in turn, raises intracellular levels of glutathione. Glutathione is made up of three amino acids, linked together like the amino acids in normal proteins. But, glutathione is a small molecule. It is important in many cellular functions including the folding of proteins into their correct structures. It also is an antioxidant (Kehrer and Lund, 1994) that detoxifies free radicals directly by interacting with them. And, it also is an important contributor to the detoxification of many free radicals and foreign chemicals by enzymes (Hayes and Pulford, 1995; Talalay et al., 1995). For example, it aids in the enzymatic detoxification of lipid peroxides and hydrogen peroxide.
The synthesis of glutathione is often limited by the supply of free cysteine. The concentration of free cysteine is very low in plasma. Low levels of glutathione lead to a decrease in intracellular antioxidant activities, and a decrease in the activities of the enzymes which depend on correct intracellular oxidation-reduction potential for their structure and activity.
There are no large clinical trials that demonstrate health benefits from glutathione or NADH supplementation. But a decrease in glutathione levels has been found in aging animals and humans, and in various disease states (Meydani et al., 1995). Glutathione levels decrease in the lens of the eye as we age. Lower glutathione levels have been found in the lens, spleen, liver, kidney and heart of old mice compared to young mice. In one study, half of elderly subjects had lower blood glutathione concentrations than younger subjects. There is a positive correlation between tissue glutathione levels and lifespan in mice. Glutathione inhibits liver cancer growth in humans and oral cancer in hamsters. Thus, the decline in glutathione levels with age may be related to the increase in cancer.
The decrease in glutathione levels with age also may partly explain the age-related decrease in immunity. And, decreased glutathione may partly be responsible for the liver's loss of detoxification ability. This loss is found in most mammals, including humans. Low glutathione levels are associated with arthritis, diabetes, heart disease and cataracts.
In clinical studies in the elderly, higher glutathione levels are associated with fewer illnesses and the perception of improved health. Finally, dietary supplementation with glutathione, or with supplements that raise glutathione levels, appears to improve the immune response in humans and experimental animals.
NADH (a form of nicotinamide adenine dinucleotide) is a coenzyme that assists enzymes involved in energy production within mitochondria. NADH plays an important role in the generation of ATP, the body's energy currency, and has been found to be deficient in several age-related degenerative diseases. Uncontrolled studies in Europe have found NADH beneficial for patients suffering from Parkinson's disease, Alzheimer's disease, and depression (Birkmayer, et al, 1990). NADH also is needed for the regeneration of glutathione after it becomes oxidized (Sies and Stahl, 1995; Kehrer and Lund, 1994). If NADH levels are depleted, glutathione levels also may fall. Thus, supplementation with NADH also may help restore glutathione to its active form.
Melatonin is a mammalian hormone, secreted at night during sleep by the pineal gland. Although melatonin's role as a hormone is subtle, it is clearly a potent antioxidant (Reiter et al., 1996). It is both water- and membrane-soluble, and acts as an antioxidant in both lipid and aqueous environments. Dosages that raise blood levels of melatonin to higher-than-normal levels protect against agents that damage cells by generating oxygen radicals.
These include ionizing radiation, the chemical carcinogen safrole, the diabetes-inducing toxin alloxan, the herbicide paraquat, bacterial lipopolysaccharide, and the liver toxin carbon tetrachloride. Melatonin also protects against cataracts caused by buthionine sulfoxamine, a drug that blocks the production of glutathione.
Melatonin is absorbed readily when taken orally, and has very low toxicity. In fact, few if any negative side effects have ever been reported for melatonin. In addition to its antioxidant effects, Melatonin has been proposed as a regulating agent for the biologic aging clock. A previous study suggested that Melatonin may be able to extend lifespan in rodents. Our study will seek to determine if this is possible.
The Mystery of Aging
Two additional theories of aging also will be examined during The Lifespan Project.
The questions? How does glycation and hormone depletion influence longevity? Why do we age? In addition to the free radical and energy-depletion theories of aging, there also are the glycation and hormonal theories. Each theory proposes different biochemical mechanisms for aging. It's possible that all four are right, that their concerted action produces the symptoms of aging.
Anthony Cerami and colleagues proposed the glycation theory of aging. This theory postulates that cellular damage from glucose (blood sugar) is a factor in aging. Diabetes, which is characterized by abnormally high levels of blood glucose, is probably a form of accelerated aging. High blood glucose levels are associated with long-term neurologic problems, kidney damage, atherosclerosis, loss of vision, cataracts and impaired cellular immunity (Ziyadeh. & Cohen, 1993; Anonymous, 1993; Rossetti et al., 1990).
High insulin levels often are found in people with heart disease, atherosclerosis and high blood pressure (Ferrari & Weidmann, 1990; Stout, 1990; Ducimetiere et al., 1980). These are many of the diseases and complications that occur in old age.
In fact, one of the characteristics of human aging is a progressive rise in blood glucose levels. Blood glucose rises because insulin becomes less effective in causing glucose uptake by muscle and fat cells.
Glucose reacts slowly with proteins, fats, lipids and even with the genetic material of our cells (Lee & Cerami, 1992). With the passage of time, it forms toxic chemicals that have been given the name "advanced glycation end products," or AGEs (Baynes, 1991). This same process takes place much faster through the heat of frying or broiling, which is what gives cooked meat its brown color. During this process, reactive glucose forms free radicals which continue and amplify the reaction, enlarging the damaged area. Over a lifetime, this kind of damage accumulates, even in people without diabetes. The damage may even be involved in the loss of neurologic functions during aging.
Recent research has shown that the effects of many small strokes in older people accumulate over the years to finally rob us of short-term memory. The neurofibrillary tangles and senile plaques in the brains of patients with Alzheimer's disease contain AGE, while little if any of these products are detected in healthy brain regions, even within the same brains as the afflicted persons (Smith et al., 1994).
August Cover Story Continued