Nicotinamide Induces Rejuvenation
In Human Cells
This remarkable B-vitamin assumes ever more
importance in terms of the aging process
By Will Block
hat is it about nicotinamide? Regular readers of this magazine know that the nicotinamide molecule - a close relative of the B-vitamin niacin, with similar vitamin activity - may play an important role in certain biochemical mechanisms that affect the lifespan of a variety of creatures on the evolutionary tree of life. This is because nicotinamide is a chemical precursor of a molecule that definitely plays a role in those biochemical mechanisms. That molecule, nicotinamide adenine dinucleotide (NAD), is a vital cofactor in a process called gene silencing, about which we have written several times (see, e.g., "The Secret to Longevity Is Hidden Deep in the Gene Pool," Life Enhancement, November 2001).
So we know that nicotinamide is vital for human health, in terms of both its vitamin activity and its role as a precursor of NAD - and it may even play a role in determining human longevity. Now comes news, in a research paper recently published in the journal Cellular and Molecular Life Sciences, that nicotinamide can actually bring about a kind of rejuvenation of certain types of human cells called fibroblasts when they are undergoing the aging process.1 The researchers are affiliated with the Institute of Medical Science at the University of Tokyo and the Department of Chemistry at Rutgers University in New Jersey. The abstract of their paper begins and concludes with these provocative statements (don't sweat the technical terms - we'll explain them in due course):
Aging appears to be an irreversible process. Here we report that nicotinamide can induce rapid and reversible reversion of aging phenotypes in human diploid fibroblasts in terms of cell morphology and senescence-associated beta-galactosidase activity. . . . Taken together, the results suggest that nicotinamide may cause rejuvenation by restoring, at least in part, altered gene expression in aged cells through its activation of histone acetyltransferase.
Let's see what that mouthful of biological jargon means. For starters, it means that, under certain laboratory conditions, certain observable aspects of the aging process in certain types of human cells can be reversed under the influence of a certain chemical compound: nicotinamide. Does this mean that ingesting more nicotinamide will make us younger? That's impossible to say based on the results of this laboratory study, which make no such implication. Only time and further research will tell.
What the new results do imply, though, is that nicotinamide may be even more important for human health than we previously thought. Clearly there is something fundamentally important about this molecule as regards the aging process, and we need to know a lot more about it. If you're really interested in science, read on - otherwise you can skip to the end and read the section called "But What Does It All Mean?"
Phenotype Describes the Organism or Cell
Now it's time to decipher those technical terms so that we can better appreciate what the researchers were actually saying. First of all, what is a phenotype? Simply put, phenotype is the appearance of an organism - or, in this case, the appearance of a single cell - resulting from the interaction of its genotype and its environment. Uh-oh. What's a genotype? That's simply the organism's (or the cell's) genetic constitution - the sum total of all its genes, which determine all the essential physical characteristics of the organism, as well as all the fundamental physiological processes that enable it to live and develop.
The genotype remains the dominant factor in how the organism develops over time, but it is clearly not the only factor. The other factor is environment. At the moment of birth (or hatching, or whatever), the organism has a clean slate as far as its environment is concerned, but environmental factors begin to affect it immediately, and they never stop. Environmental factors include such things as what the organism eats (good food? junk food?), what it does (exercise freak? couch potato?), and what outside influences it's exposed to, such as sunlight, heat, cold, air or water pollution, and diseases.
So, getting back to phenotype, it is the sum total of the observable physical or biochemical characteristics of an organism - what it looks like in both large-scale features and molecular composition, as determined by the genetic makeup of the organism and the environmental influences that have been shaping it all its life.
The term phenotype is also used, however, in the more limited sense of the expression of a specific trait, such as stature or blood type - or, in the case of the research we're talking about here, cell morphology (the size and shape of the cell) and senescence-associated beta-galactosidase activity. Senescence mean aging, and beta-galactosidase is a type of enzyme that breaks down lactose (the primary sugar in milk) and related molecules.
Fibroblasts Give Rise to Connective Tissue
So now we know that nicotinamide affects the size and shape of certain aging cells as well as certain aspects of their biochemistry. When normal cells approach the end of their lifespan, they gradually become larger, undergo changes in shape, and exhibit increased activity of the beta-galactosidase enzymes. These changes are called markers of aging because they can be observed and measured rather easily.
The cultured human cells used in this study - diploid fibroblasts of several types - were chosen because they have well-defined lifespans and lend themselves well to observation of the phenotypic markers of aging. The term diploid means having two of each type of chromosome in the cell, so that the basic chromosome number in the cell is doubled. We need not be concerned with the implications of this fact.
Let's look at the more interesting term fibroblast, which is a cell that gives rise to connective tissue. That makes it an important kind of cell, because connective tissue is very important stuff, without which your body would be just a big blob of flesh that wouldn't be able to lift a finger for a million bucks (see the sidebar on this subject).
|What Is Connective Tissue?|
The term connective tissue refers to a number of different kinds of tissues that serve a variety of important functions in the human body. There are three major kinds of connective tissue:
- Supporting – These tissues give strength, support, and protection to the soft parts of the body. We call them bone and cartilage (without cartilage, your ears, e.g., would be loosely hanging flaps of flesh, so be grateful for cartilage).
- Binding – These tissues bind body parts to each other. We call them tendons and ligaments. Tendons bind muscles to bones; they are strong but not elastic. Ligaments bind bones to each other; they are strong and elastic.
- Fibrous – These tissues, of many kinds, are distributed throughout the body and serve as packing or binding materials for most of our organs. One type, called fascia, is a sheet or band of tissue that envelops, separates, or binds together muscles, organs, and other soft structures. Another type, called adipose tissue, is a storage medium for fat.
The primary constituent of most connective tissue is collagen, the most common protein in the human body. The protein elastin is also found to varying degrees, as well as many other organic and inorganic molecules, depending on the type of connective tissue. And all connective tissue has its origins in those vital cells called fibroblasts.
Gene Expression Is the Source of Life Functions
Now that we've fought our way through the jargon in the first part of that quote and understood what it means (go ahead, read it again, now that you're an expert), the real question is: But what does all this mean? The answer is suggested in the second part - where there's some more jargon to deal with.
Figure 1. The nicotinamide adenine dinucleotide (NAD) molecule. The portion shown in purple is the nicotinamide molecule, a precursor of NAD.
First of all, gene expression is the term used to indicate that a gene is actually doing something rather than just sitting there in the chromosome like a bump on a log. And what does a gene do when it's expressed? It directs the synthesis of a particular protein for which its own molecular structure is uniquely coded. This occurs by a complicated process that, thankfully, we need not go into.
What's important to know is that every protein (there are tens of thousands of different kinds in the human body) performs a particular life function in our cells, and it's the gene that codes for a given protein that is thus ultimately responsible for that life function. If the gene is expressed, the function is carried out; if the gene is not expressed (i.e., it is "silent"), the function is dormant - relatively, anyway. In any given cell, most genes are silent most of the time, because not everything that can happen should be happening all at once in the same place - that would be a mess. The trouble with aging is that certain aspects of gene expression change with time - drastically, in some cases - resulting in alterations of cellular function that hasten the cells' (and our) demise.
Histone Acetyltransferase Is Related to Aging
So if, as the authors say, "nicotinamide may cause rejuvenation by restoring, at least in part, altered gene expression in aged cells," how does it do that? Apparently by activating histone acetyltransferase. OK, that's the last of the technical terms we have to deal with, so here goes. Histone acetyltransferase is an enzyme (all enzymes are proteins, by the way) whose activity declines in aging cells. Its function is to chemically modify the protein "mantle" that cloaks the DNA molecule in every chromosome (this DNA-protein complex is called chromatin). The mantle consists primarily of five different kinds of proteins called histones, and modifying their structure at certain points affects the degree to which the underlying genes are expressed.
If this is starting to sound eerily familiar, it's because you have previously read about gene silencing. In gene silencing, an enzyme called Sir2p, in conjunction with its vital cofactor NAD (recall that nicotinamide is a precursor of NAD), chemically alters the histones in the chromatin mantle by removing acetyl groups from them at certain points. This results in the silencing of certain genes that would otherwise be expressed - perhaps too much so. The overexpression of these genes hastens the aging process, so silencing them retards it and extends the lifespan of the organism. (This phenomenon has been observed, so far, only in certain yeasts and worms, so it remains speculative for higher organisms.)
A biochemical signal triggered by
nicotinamide may act directly on
events that are pivotal in the
cellular aging process.
Because Sir2p (with activation by NAD) removes acetyl groups from the histones, it is called a histone deacetylase. And what does our new friend, the enzyme histone acetyltransferase, do (with activation by the NAD precursor nicotinamide)? It does the opposite: it adds acetyl groups to the histones at certain points. One enzyme taketh acetyls, the other giveth acetyls.
Does Nicotinamide Affect Lifespan?
Uh-oh - that sounds confusing. NAD is an activator for one process, but its precursor, nicotinamide, is an activator for the opposite process. Does that make sense? It does to a molecular biologist. The biochemical dynamics of a cell are immensely complex, with thousands of different kinds of reactions occurring simultaneously. A given kind of molecule, such as nicotinamide, may participate in any number of different kinds of reactions, going in different directions, simultaneously. It would be naïve to think that it must follow just one path toward just one outcome - biochemistry doesn't work that way.
We can be pretty sure that
nicotinamide plays an important
role - possibly a key role - in
some aspects of human longevity,
and that it’s probably wise to
be sure we have ample amounts
of it in our daily nutrition.
Thus, although it may be surprising that nicotinamide seems to play contradictory roles, they're really not contradictory at all - they're part of the exquisite balancing act among all the different chemical reactions going on all the time in all our cells. In a sense, that balancing act is the very definition of life.
And what do the results of this study say about the effect of nicotinamide on the lifespan of human diploid fibroblasts under the conditions of the experiment? Nicotinamide had virtually no effect on the lifespan of those cells, but only on their aging phenotypes. This led the researchers to speculate that nicotinamide does not play a role in cellular replication, the biochemical "machinery" by which cells reproduce, making copies of themselves. Instead, they believe that nicotinamide's cell-rejuvenating effect derives from processes unrelated to NAD.
Only Nicotinamide Has a Significant Rejuvenating Effect
The researchers tested numerous nicotinamide-related compounds, including niacin, NAD, and a number of molecules similar to NAD, to see if any of them had a cell-rejuvenating effect similar to that of nicotinamide itself. With one exception, none of them had any such effect. The exception was NAD, which induced a similar but weaker morphological change in the fibroblasts at one concentration level. Despite that fact, the researchers ruled out the possibility that nicotinamide's effect could be attributed to an interaction with an NAD-dependent cellular metabolic process, such as gene silencing.
On the contrary, they surmised that a biochemical signal triggered by nicotinamide acts directly on events that are pivotal for the expression of various aging phenotypes, and the evidence suggests that the key events are likely related to the genes that are influenced by nicotinamide's stimulation of histone acetyltransferase activity - a surprising discovery.
The researchers noted, furthermore, that nicotinamide's rejuvenating effect was dose-dependent, meaning that the effect grew in proportion to the amount of nicotinamide used (up to some point, of course, beyond which it became toxic, as any substance will if present in too great an amount). The effect was also reversible, meaning that the aging phenotypes could be made to wane or wax depending on the presence or absence of nicotinamide in the culture medium. Remarkable!
But What Does It All Mean?
We're still left with that question, aren't we? And the answer is: we don't really know, because so much more needs to be discovered before it can all become clear. We can be pretty sure, however, that nicotinamide plays an important role - possibly a key role - in some aspects of human longevity, and that it's probably wise to be sure we have ample amounts of it in our daily nutrition. Supplementing with nicotinamide carries no significant risk, and it just might be a steppingstone to a longer, healthier life. (For more on this marvelous molecule, see "Nicotinamide Links Calories, Genes, and Antiaging" in Life Enhancement, September 2001.)
|Nicotinamide is important in regulating certain aspects of gene expression related to longevity.|
Nicotinamide is also known as niacinamide. There's no difference between them. Niacinamide is a derivative of niacin (it does not, however, product the notorious "flushing" effect of niacin), which is also known as vitamin B3.
- Matuoka K, Chen KY, Takenawa T. Rapid reversion of aging phenotypes by nicotinamide through possible modulation of histone acetylation. Cell Mol Life Sci 2001;58:2108-16.
Will Block is the publisher and editorial director of Life Enhancement magazine.