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Antioxidant Cocktail Update: Part 5 Venturing beyond oxygen radicals. An Interview with Dr. Lester Packer
By Richard A. Passwater, Ph.D.
As we noted at the close of our last column (WHOLE FOODS, January 2000), the most exciting and important new information about the extraordinary nutritional compounds called antioxidants is that they are involved in genetic expression. In this fifth and final installment of our series on this topic, we will explore why this is relevant to aging, cancer, heart disease, arthritis and, in fact, most non-germ diseases; all of these are greatly influenced by our genes.
Our guest, as he has been for the past several months, is Dr. Lester Packer, a professor in the Department of Molecular and Cell Biology at the University of California at Berkeley. Dr. Packer received his Ph.D. in microbiology and biochemistry from Yale University in 1956 and has been at Berkeley since 1961.
Recognized as one of the world's leading researchers on vitamin E and other biological antioxidants, he has written or edited more than 70 books and over 700 articles, mainly for trained scientists. His latest book, The Antioxidant Miracle, takes a more popular approach and is intended to be read by the general public.
Passwater: Dr. Packer, I have just read a survey by the Hartman Group; it reports that 75% of the people interviewed claim they know what an antioxidant is as opposed to 53% who know what the term "RDA" means and 10% who know what nutraceuticals are. It may not be too many years before most people know what NF-kB is. I remember the gleam in your eye a few years ago (I think it was right after you had received the VERIS Award for your research on vitamin E, and you mentioned your new research on the role of antioxidants and genetic expression).
At that time, your research just was beginning to open up a new understanding of the importance of antioxidants. As medical researchers were finally beginning to understand the "classical" role of antioxidants in terminating harmful free radicals, you were opening up a new and possibly more important area. The next thing I knew you were scheduling a conference in Kona, Hawaii to bring together leading genetic researchers and antioxidant researchers to get them talking to each other. Experts from each field had to start at level one to bring their opposite numbers up to speed. After 30 years of studying free radicals, I and others in our field had to learn the ins and outs of "up regulation" and "down regulation." Many of our readers still may be lacking any detailed knowledge of these concepts; would you be kind enough to tell us a little about the importance of antioxidants and gene regulation or genetic expression.
Packer: Since the days you are referring to, a lot has happened. We now realize that virtually every pathway involved in cell signaling used to turn on genes involves redox and oxidative-sensitive steps. This is all the way from the membrane to the gene, from the receptors that are associated with membranes, to the secondary signals that the cell uses to turn on or turn off genes (up-regulate or down-regulate various gene products). This is an exciting development. It has been slow to come; different systems have been looked at different times, but now all the major systems have been found to have certain steps that are sensitive to oxidants. For example, sulfhydryl groups are critical for the binding of activated transcription factors to DNA.
We have learned that many of the major pathways involved in signal transduction and gene expression can be regulated by oxidants and by redox-sensitive steps. Major systems affected by oxidants and redox-sensitive steps appear in Figure 2 (Page 52). Nuclear transcription factor NF-kB, is involved in inflammatory responses, APl is important for cell growth and differentiation and p53 is a gene whose disruption is associated with more than half of all human cancers. The p53 protein guards a cell cycle checkpoint, and inactivation of p53 allows uncontrolled cell division.
In order for transcription factors to bind to DNA, they require a reducing environment. Antioxidants, which are redox reactive substances, can help to provide a reducing environment, allowing activated transcription factors to bind DNA and to turn genes on and off. Thus, network antioxidants can regulate the way in which genes are expressed. This is very exciting, and obviously this must be even more important than the direct scavenging of radicals.
If there is an oxidizing environment, you can't bind to DNA, you can't turn genes on and off. Antioxidants-which are redox reactive substances, at least those that are part of the network and all the ones we have been talking about-are part of the network with the exception of the carotenoids, which do not work by redox-sensitive mechanisms. They are basically "sinks" for free radical reactions. These network antioxidants now regulate the way in which genes are turned on and off. This is very exciting, and obviously this must be even more important than the direct scavenging of radicals.
In chronic and degenerative diseases-the most important of which is aging itself because aging is an incurable disease we see these genetic expression processes going on. They need to be regulated, minimized and controlled throughout our lives. Antioxidants play an important role in that process. We could spend a lot of time talking about different systems that have been
identified to be important in signal transduction and gene expression. NF-kB happens to be one of them because it is a major transcription factor involved in the turning on and off of perhaps 400 genes that mostly are important in inflammatory system like the production of sell adhesion molecules, nitric oxide and tumor necrosis factor (TNF). This system probably has received most of the studies in this regard because most it is very clear that a variety of different ways can be used to activate NF-kB, and almost all of them involved reactive oxygen species.
As noted, ,antioxidants play a key role in regulating the activation of NF-kB. This is important because NF-kB is found in many parts of the body. It is in the cells of our skin; if they are exposed to UV light, then NF-kB is activated. It is found in the cells of the kidneys of people who have diabetes because diabetes is an oxidative stress disease. Everywhere you look you find NF-kB.
Every other year, I go to an international summer school in Greece. At these sessions, we invite many famous people to lecture, and we have postdoctoral and young scientists attending. It is a very exciting program set in an informal atmosphere. At one of these meetings, we hosted Dr. Yasutomi Nishizuka , the person who is credited for having discovered protein kinase C. It is a very key component in the signal transduction pathway. There have been about 20,000 studies on protein kinase C. There are 10 known supergene families of protein kinase C, each one representing a different isoform.
When he was with us, Dr. Nishizuka never talked at all about the role of oxidation or of antioxidants and protein kinase C, because in those days researchers still were trying to identify which components were members of the family and how the various family members differed in terms of how they worked. After most of these issues were resolved, suddenly it began to surface that oxidation of key residues like tyrosine residues and tyrosine phosphorylation played a great importance in the activation of protein kinase C.
Oxidants and antioxidants are regulatory factors. But we didn't think about this aspect in the beginning. Now, we are paying attention to fine-tuning how genes are regulated. Oxidants and antioxidants always are there, and if you have an imbalance you can upset the way in which genes are expressed. I could go on and talk about this for a long time because I think it is where most of the antioxidant research is going to turn in the next century. It obviously is the direction we are headed, and it is a very exciting new direction.
We have to remember too that only 30 or 40 years ago it was not yet possible to use instruments that the chemists and physicists had been using for some time. These instruments now have become indispensable in showing that free radicals are important in biological systems.
We discovered in the 1970s that free radicals were produced in exercise. That was a ground-breaking discovery. Even today, we don't know quite as much as we would like about the role of free radicals and antioxidants in exercise, but it is becoming a major area of investigation by the American College of Sports Medicine, the biggest organization devoted to exercise science in America. This work is going on all over the world, and it is becoming increasingly clear that genes are affected in exercise, particularly in exercise training. Further, we are learning that these genes are being modulated by oxidants and antioxidants, so we have a lot to chart out there in the next century. It is going to be a very exciting time for our young colleagues who are now developing careers. "Spectacular" is the word that best describes what we are going to learn in the next decade or two in this area. I think network antioxidants are going to become a household word along the way.
Passwater: In the previous installment of this series, I mentioned that Dr. Arstila described how Pycnogenol was involved in the activation of NF-kB (WHOLE FOODS, January 2000). Would you review for us, in general, what exactly is involved in the activation of NF-kB?
Packer: The nuclear transcription factor NF-kB is important in the expression of many genes whose proteins are involved in the control of apoptosis (cell suicide), in the development of B and T cells, in antiviral and bacterial responses, in responses to multiple stresses, in embryonic development and in inflammatory responses.
Downstream products of NF-k13 activation include inflammatory cytokines (messenger molecules) important for leukocyte activation and leukocyte recruitment, tumor necrosis factor (TNF), nitric oxide synthase (NOS), and hence regulation of vascular tone, cell adhesion molecule expression involved in inflammatory response, and viral activation such as in HIV.
Ultraviolet radiation, cigarette smoke, ozone and many other stimuli activate NF-kB. This appears to be mediated through the production of reactive oxygen species (ROS). NF-k13 exists in the cytosol as a preformed trimeric complex. The P50/P65 protein dimer is associated with an inhibitory protein known as IkB. Oxidants trigger a change in the cell that results in phosphorylation of the IkB subunit. After IkB is phosphorylated, a process of the proteolytic digestion of this sub-unit is activated.
When the inhibitor sub-unit is dislodged from the P60/P65 heterodimer, the activator NF-kB can migrate to the nucleus and bind to DNA, thereby initiating transcription.
Reduced thioredoxin is an essential component contributing to the reduction of activated NF-kB, allowing it to bind to DNA. There are many redox-sensitive steps in the signal transduction pathways. Oxidants can be counteracted by antioxidants that modulate NF-kB activation.
Passwater: OK, let's give our readers a quick review of the entire antioxidant role.
Packer: I guess we can say that the recycling of electrons through the antioxidant network sends signals to redox-sensitive transcription factors (NF-kB, API and P53). These factors control the expression of protective genes that repair damaged DNA, power the immune system, arrest the proliferation of damaged cells, and induce apoptosis.
Apoptosis is a gene-directed process of cellular deletion that establishes an equilibrium between cell birth and cell death. This is an important defense against many types of biological damage such as radiation, viral infections, drug toxicity, and cancer. By this process, the cell can exert a direct control on its own death, sacrificing itself to protect its host. Apoptosis of cancer cells can be blocked by NF-kB proteins. Antioxidants inhibit NF kB, thus helping to fight cancers.
As we age, cumulative, ongoing free radical insults desensitize the activation thresholds of these redox-modulated transcription factors. Our genes may remain functional, but the switching system that activates them deteriorates and this drift contributes to immune dysfunction, cancer, and chronic disease.
By supplementing the antioxidant network, we accomplish two things: 1. we reduce the rate of accumulation of damaged DNA; and 2. we potentially normalize the age-related decline in the regulation of the redox-sensitive gene expression.
Passwater: Dr. Packer, thanks for taking this time and sharing your knowledge with us. Meanwhile, even though we covered so much ground that this series has required five separate installments, we never did get to discuss your list of the top 10 achievements of your career. Maybe we can chat again next year and try to cover at least the top five.
But, at the rate you are turning out new research, we should recognize that any such list will only be a work in progress, awaiting the next great accomplishment to come out of your laboratory. In the meantime, Dr. Packer, your book, The Antioxidant Miracle, has good advice that will help all our readers and their customers protect themselves against free radicals of all types and regulate genes to maintain optimal health. WF
© 2000 Whole Foods Magazine and Richard A. Passwater, Ph.D.
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