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Chapter 2: Antioxidants as Drugs against Aging
The First Antioxidant Drugs Suggested: BHT and Others
One of the earliest classes of substances put forward seriously as drugs against aging are the antioxidants, Vitamin E and BHT being the most well-known. Beginning about 1956, Dr. Denham Harman, of the University of Nebraska, put forward the hypothesis that at least some of the degenerations of aging arose through the same processes as those of radiation damage: that is, highly reactive chemicals (in the case of aging, created by our normal metabolism rather than radiation). A corollary of this hypothesis would be that drugs which protected against radiation would also protect against aging; antioxidants are a large class of such substances, well known to protect against radiation damage, and therefore against aging as well.
Since 1956 Harman himself has written extensively on his theory, and can produce some evidence for it. For instance, unsaturated fats should cause more chemical reactions of the kind antioxidants protect against (free radical reactions) and therefore animals fed high levels of unsaturated fats should show a higher mortality rate, which is indeed the case. One can also construct an argument that lipofuscin, a pigment that accumulates in animal tissues as they age, has formed because of these same free radical reactions.
As longevists we are interested in such drugs for their use on man. What kinds of evidence are there for effectiveness of antioxidants in aging? What needs to be done to find antioxidants suitable for use in man?
Harman's first experiments tested several drugs for effects on the lifespan of AKR and C3H mice. He obtained a lifespan increase in his mice of about 20 percent. The antioxidant BHT, and a radioprotective drug MEA, were tested. A second series of experiments, published in 1968, studied MEA, BHT, and several other drugs known to inhibit free radical reactions of the kind that, by Harman's theories, should play a role in aging. In some experiments, with some drugs and strains of mice, Harman could obtain an increase as high as 30 to 50 percent. Table II on the next page shows these increases.
Other workers have also reported lifespan increases in mice fed antioxidants. Alex Comfort in NATURE (229 (1971) 254-255) confirmed that another antioxidant, ethoxyquin, would prolong the lifespans of C3H mice. Buu-Hoi and Ratsimanmanga (COMPTES RENDUS SOCIETE BIOLOGIE 1180-82, 11 July, 1959) testing only a small number of Wistar rats, showed that still another antioxidant, NDHGA (nordihydroguaretic acid), would prolong the lifespan of rats if fed throughout most of their lifespans.  Some comments should be made about these results. First, the mice studied were not all fed the same diets, nor were they all the same strain of mouse. This may be important. Harman's first series of experiments were carried out with AKR mice and C3H mice. These mice are very shortlived; they were bred especially for susceptibility to cancer, and cancer researchers often use them a lot to study cancer. Someone who wished to argue against Harman's theories could point out that his drugs may have acted against cancer rather than aging. Similarly his later experiments with a third strain, LAF mice, involved feeding the mice a special diet (which he calls "semisynthetic") in addition to the drugs. An examination of his results shows that the control mice on a semisynthetic diet died sooner than those fed a normal commercial diet. Indeed, even with the best of the drugs (BHT), mice on the semisynthetic diet did not live as long as control mice on a commercial diet.
For all of these reasons, some questions do exist about whether or not Harman has obtained a true lifespan increase with his experiments. In fact, the only experiment for which this criticism does not hold is the one using MEA. However, Harman has shown that antioxidants will protect against at least three separate kinds of deleterious influences: bad heredity (susceptibility to cancer in AKR or C3H mice), bad diet (the semisynthetic diet), and (including the experiments of others) radiation. In the sense that they did increase lifespans, these experiments deserve attention. Percentage increases like those Harman has obtained, even if they only raise our average lifespans and not our maximum possible lifespan, should interest us considerably. I will say, though, that Harman's experiments do provide a border- line case for the lifespan criterion explained in the Introduction.
Of the antioxidants studied so far, what information exists as to their safety in man? For some antioxidants Harman has studied, very little work on toxicity of any kind has been carried out. Neither of the drugs DDC or Diaminodiethyl DS has yet been tested for toxicity. However Vitamin E, BHT, and ethoxyquin have been studied for their toxicity as antioxidants to be added to our food, and some work has also been done on NDHGA. The drug MEA has also been studied as a radioprotective drug for human beings; since it will be discussed separately I shall omit it here.
VITAMIN E
At present many theoretical arguments suggest that Vitamin E may have at least some effect on aging; there are even experiments with cell cultures and invertebrates which support these theories. Gershon (MECHANISMS OF AGING AND DEVELOPMENT 1(1972) 257-264) has shown that Vitamin E will increase both mean and maxiumum lifespan of nematodes. However only scanty evidence exists that Vitamin E will have similar effects on mammals. Two experiments are suggestive. McCoy in 1943 (ARCHIVES OF BIOCHEMISTRY 2(1943) 474) as part of work on lifespan increases in rats, fed male and female rats a diet enriched with wheat germ and found an increase of 20 percent over his controls. Unfortunately this result is clouded by the probability that his control diet was deficient in Vitamin E, which is an essential vitamin. A second experiment reported by Harman studied the effect of Vitamin E on the lifespan of LAF mice. The increase produced was small and not statistically significant; at 20 months 8.8 percent of control mice survived, compared to 13 percent of the Vitamin E mice. Lifespan increases in the same experiment with BHT were far greater, with better than 60 percent survival of treated mice at the same time.
At one time, some scientists raised doubts about high doses of Vitamin E because they increased blood cholesterol levels in rats, and so might cause increased heart disease. More recently, work reported in the NEW ENGLAND JOURNAL OF MEDCINE (328(1993) 1444-9; 1450-6) strongly suggests that Vitamin E at doses of 100 IU or above will protect humans against heart and artery disease. Unfortunately it does not discuss lifespans as such (does it simply change the cause of death?), nor does it discuss doses higher than about 400 IU/day (see the Introduction).
On the other hand, the evidence for safety of Vitamin E is very strong. Vitamin E has already been used in human beings for several clinical conditions. Boyd (PROCEEDINGS OF THE ROYAL SOCIETY OF MEDICINE 44(1951) 985) reports treating patients with Vitamin E at 400 mg/day for 3 months with no ill effects; Haeger (VASCULAR DISEASES 5(1968) 199) reports similar treatment at 300 mg/day for more than 2 years. Hoffer (JOURNAL OF ORTHOPEDIC PSYCHOLOGY 3(1972) 15) reports treatments of more than 800 mg/day with no measurable ill effects.
Since suppliers of Vitamin E often measure it in terms of I.U's (International Units) readers may wish to know that 100 I.U. Vitamin E equals about 2 mg.
ETHOXYQUIN
A third antioxidant put forward for use against aging is ethoxyquin. Evidence for its efffectiveness comes from two experiments, the 1968 experiment by Harman, in which 74 percent of treated LAF mice survived for 20 months on the semisynthetic diet, as compared to 8.8 percent of controls, and the experiment of Comfort with C3H mice. With ethoxyquin, increased lifespan of treated animals compared to controls is quite clear.
Unfortunately ethoxyquin has severe toxicity problems. The earliest published study of toxicity of ethoxyquin was done by RH Wilson and F de Eds (JOURNAL OF AGRICULTURE AND FOOD CHEMISTRY 7: 205-206). They studied the chronic toxicity of ethoxyquin in albino rats at concentrations from 0.4 percent by weight of diet down to 0.1 percent and 0.0 percent. Although they found no difference in lifespans of treated and untreated rats, they found also clear injury to kidneys of animals fed the higher concentrations (0.2 and 0.4 percent) ethoxyquin. Kidneys showed irregular areas of fibrosis and signs of chronic kidney disease; liver cells showed changes in structure increasing in proportion to the amount of ethoxyquin received, and thyroid glands also showed signs of damage. Other studies of toxicity have basically confirmed this one.
Moreover the experiments showing increased lifespans of treated mice do not contradict these signs of toxicity. The study by Wilson and de Eds looked at toxicity of ethoxyquin when given for long periods, just the kind of treatment needed for aging. Harman's mice were fed semisynthetic diet, which decreases survival; Comfort's experiment studied ethoxyquin on C3H mice, known to have a short lifespan. We therefore cannot argue that lifespan increases in LAF or C3H mice will in any way prove that ethoxyquin might not be toxic to human beings when taken longterm. Ethoxyquin is unsuitable as a drug for prolonging our lives and could actually be dangerous on longterm administration.
BHT
Finally BHT should be discussed. Of all antioxidants studied so far, BHT perhaps has the best record. For its effectiveness we have several experiments of Harman, which show that at a minimum BHT has a protective effect against several deleterious environments. Toxicological studies of BHT treated animals suggest that its record is fairly good, though not at all perfect. One series of experiments (Deichmann et al AMA ARCHIVES OF INDUSTRIAL HEALTH 11(1955) 93) studied the toxicity of BHT at concentrations of 0.1 percent by weight of diet and found no effect on any of the parameters studied.
However in 1959 Brown et al (AUSTRALIAN J OF EXPERIMENTAL BIOLOGY AND MEDICAL SCIENCE 37(1959) 295, 533) called these experiments into question by observing that they had all been carried out using diets low in fats, unlike the normal human diet (which has at least 20 percent fat content). When they repeated the experiment on high fat diets they found some significant signs of toxicity, of which the most serious is that combination of high fat diets with BHT caused a marked rise in blood cholesterol levels in treated animals compared to controls. Since high blood cholesterol may correlate with heart disease we would have to take this seriously. This may mean very little; recall the similar questions raised about Vitamin E. However, even though many doctors do argue vehemently that cholesterol levels do not relate to heart disease in any simple way, these results should still make us cautious. At present, therefore, we have at least reasonable indications that BHT will be safe on low fat diets; however on high fat diets questions exist about its safety in longterm use.
NDHGA
As a drug for human use, NDHGA has some evidence of effectiveness and a long tradition of actual use as a food antioxidant. Effects on longevity appear good. Out of 12 controls at 796 days of age, 2 rats survived, while 8 rats out of 12 survived among the treated animals. Unfortunately the small number of rats studied makes this result suggestive but in no way conclusive. Dosage was notably less than that of mice in Harman's experiment: 20 mg/kg of food as against 1 gm/kg. Despite this low dosage, apparent increase in lifespan was relatively high. As mentioned, NDGHA has a long tradition of use as a
natural food antioxidant. It is made from an evergreen desert shrub, Larrea divarticata.
At concentrations of more than 0.5 percent by weight of diet, rats will develop inflammations in their caecum (the end of their intestines) and show inhibited growth. A different experiment has shown much worse results at these levels; in one 2-year test on rats, the rats developed massive hemorrhages in the caecum. Studies on mice at similar concentrations showed no deleterious changes in weight or tissues. At present there is little information on metabolism of NDHGA, although some studies have been made of its biochemistry in vitro. We can compare these results on toxicity with the dosage of the drug which may have an effect on longevity. Dose for longevity was about 0.02 percent; the lowest level causing signs of toxicity was
- 5 percent, about 20 times the therapeutic dose. NDHGA checks out as very probably safe, but at the same time we would like more work on its effectiveness, since 12 animals is a only small test sample.
NDHGA has also received surprisingly little interest from longevists generally. The experiment in which Buu-Hoi and Ratsimamanga showed that it increased lifespan was published in French in the French scientific literature. This may have delayed its notice by English- speaking scientists.
SOME OTHERS
Studies on the lifespan of mice receiving various supplement antioxidants have continued. Unfortunately, up to now no lifespan studies have been done on many of the popular antioxidants sold in health food stores, such as the proantocyanins, bioflavonoids, lycopenes, and other antioxidants from vegetables. However, two other substances have had lifespan tests.
J Heiklen and E Brown published a study of diethylhydroxylamine (which goes by the initials DEHA, NOT than DHEA!) in J GERONTOLOGY (42 (9)(1987) 674-680). They found the greatest effect on the smallest dose they tried, 10 mg/day, with a 7.5% increase in average age of death. This was 675 days for male test mice versus 599 days for controls, and 738 for female test mice versus 685 for controls. The relatively small dose is the most notable point about DEHA, although NDHGA works in mice on a similarly low dose. Another test of a different antioxidant (EMHP, 2-ethyl-6-methyl-3- hydroxypyridine HCl) found an increase of 23% in average lifespan of female test mice (NM Emmanuel QUARTERLY REVIEW OF BIOPHYSICS 9(1976) 283-308). At present neither drug is easy to obtain in a form suitable for us.
AND FINALLY, VITAMIN C?
One group of researchers have published a study showing an lifespan increase in mice with Vitamin C: HR Massie, VR Aiello, TJ Doherty, in GERONTOLOGY (30(1984) 371-375) describe their experiment with C57Bl/6J mice, a normally long-lived strain. They found an increase in lifespan by 8.6% (and if your computations count the early death of two control mice then the increase is 20% --- but the control mice failed to live as long as in other experiments done by this team).
It's reasonable to ask what this experiment may mean. For our use it had two problems: first, the doses scaled up by body weight could come to as high 100 grams per day; at best, 14 grams a day. Second, mice normally make Vitamin C themselves, although these experimenters cite papers suggesting that their ability to do so goes down as they age. However, this still remains a major metabolic difference between humans and mice. Not only that, but the only lifespan experiment done on animals that DON'T make Vitamin C showed a lifespan DECREASE. I discuss these issues more fully in Appendix 4. Vitamin C may prove to be one of the few cases in which our metabolism, and that of our test animals, differs so much that we cannot easily extend a result true for mice to one true for human beings.
Prospects for Use:
Of all the drugs we have considered, the two best prospects as antioxidants against aging are probably NDHGA and BHT. Both are easily available as food grade antioxidants, so that supply problems will not arise even without prescriptions. NDHGA stands out for the surprisingly low dosage needed in order to obtain an effect; however as yet only one experiment has been carried out on NDGHA, so that evidence of effectiveness is less strong than for Vitamin E. For BHT we need much more detailed study, with animals other than rats and mice, of toxicity on different diets, to help assess its toxicity in man before anyone actually takes it; for NDGHA we want more detailed studies of toxicity and another larger test of effectiveness. Financial support from the longevist and immortalist community for work of this kind would be well spent.
For human use against aging, we lack all knowledge of just what dosage will give the same effect on aging in human beings as the doses given to mice affect their aging. As with the other antiaging drugs, the best suggestion would be to assume an increase of dosage by the 2/3rds power of body weight. Harman's experiments with BHT (J. GERONTOLOGY 23(1968) 476) used 0.5% by weight of the diet of his mice; normal mice take about 3 grams of food daily, hence the mice received 0.015 grams of BHT. Using the same 2/3rds rule, we get a dose of about 2.4 grams/day for human use; a dose of 2.5 grams (2500 mg) would probably serve.
Though no one would ever eat so much simply in their food, this is not really a large dose; many people take as much or more Vitamin E or Vitamin C. As a dose it works out to less than 50 mg for every kilogram of human weight. At least one test of toxic action of BHT in female monkeys used doses of 50 mg/kg-weight for 2 years and found no sign of any ill effects upon the female monkeys or their offspring (cf. AL Branen, J. AM OIL CHEMISTS SOC 52(1)(1975) 59-62). Remember, though, that just as with any substance, even water, too much becomes toxic: the acute lethal dose of BHT comes to about 2 grams per kilogram body weight (that is, 120 grams for a 60 kg man).
TO LEARN MORE:
Basic papers describing effects of antioxidants on lifespan:
Harman, D, "Free radical theory of aging: Effect of free radical reaction inhibitors on the mortality rate of male LAF1 mice", JOURNAL OF GERONTOLOGY 23(1968) 476
Buu-Hoi, NP; Ratsimamanga, "Action retardante de l'acide nordihydro- guaretique sur le viellissement chez le Rat", COMPTES RENDUS SEANCES SOCIETE BIOLOGIC 153(1959) 1180
Heicklen, J; Brown, E, "Increase in life expectancy for mice fed diethylhydroxylamine (DEHA)", JOUR GERONTOLOGY 42(9)(1987) 674-680
Emmanuel, NM, "Free radicals and the action of inhibitors of free radicals under pathological states and aging in living organisms and in man", QUARTERLY REVIEW BIOPHYSICS 9(1976) 283-308
Massie, HR; Aiello, VR; Doherty, TJ, "Dietary Vitamin C improves the survival of mice", GERONTOLOGY 30(1984) 371-375
Some papers on toxicity of several antioxidants:
Lehman, AJ et al, ADVANCED FOOD RESEARCH 3(1951) 197
Day, AJ et al, "The effect of the antioxidant butylated hydroxytoluene on serum lipid and glycoprotein levels in the rat", AUSTRALIAN J EXP BIOL MED SCI 37(1959) 295
Brown, WD et al, "The effect of the level of dietary fat on the toxicity of phenolic antioxidants", AUSTRALIAN J EXP BIOL MED SCI 37(1959) 533
Some papers on the health benefits of large doses of Vitamin E:
MJ Stampfer et al, "Vitamin E consumption and the risk of coronary disease in women", NEW ENGLAND J OF MED 328(1993) 1444-1449
EB Rimm et al, "Vitamin E consumption and the risk of coronary heart disease in men", NEW ENGLAND J OF MED 328(1993) 1450-1456
PM Farrell, JG Bieri, "Megavitamin E supplementation in man", AMERICAN J OF CLINICAL NUTRITION 28(1975) 1381-1386
| This article contains chapters from the book, A GUIDE TO ANTIAGING DRUGS, published by PERIASTRON.
Dr. Donaldson aimed to provide, in the GUIDE, a discussion of both the good points and the bad points, of every drug shown by experiment to prolong the healthy lifespan of some mammal. The mammals involved must normally reach at least the average lifespan of their species.
This Web Site provides only samples of only part of the GUIDE, which discusses other drugs also. | |