By David N. Leff
Recommended physical exercise for a long and healthy life is as follows: With both hands, grasp the edge of the table at mealtimes and push back firmly. In other words, lower your caloric intake.
¿Calorie restriction is the only intervention shown to extend the life span of mammals,¿ observed biochemist Stephen Spindler at the University of California, Riverside campus. ¿In very old animals,¿ he recalled, ¿we found that calorie restriction could reverse the negative changes in gene expression that had accrued over a lifetime of normal eating. What¿s more, it reversed about 70 percent of those negative changes almost right away.¿
Spindler is senior author of a paper in the current Proceedings of the National Academy of Sciences (PNAS), dated Sept. 11, 2001. Its title: ¿Genomic profiling of short- and long-term caloric restriction effects in the liver of aging mice.¿
¿Many scientists, myself included,¿ Spindler told BioWorld Today, ¿thought that caloric restriction [CR] prevented negative age-related changes in gene expression. Instead, what we find now is that it changes gene expression to be more like young-gene expression, and does it much faster than we¿d ever thought. The other important conclusion of our work is that we should be able to screen drugs, develop pharmaceuticals, and test those very quickly in young or old animals ¿ or presumably young or old humans.
¿Reproducing these genetic biomarkers, the effects of CR,¿ he continued, ¿gave us an initial microarray screen that we¿ve never had before ¿ to seek drugs that might slow the onset of age-related diseases, and perhaps extend life span as well. We knew that calorie restriction delays the onset of age-related disease,¿ he went on. ¿The major age-related killer diseases are cancer, heart disease and diabetes. That¿s what humans die of. Absent infectious diseases or accidents, about 80 percent of us will succumb to heart disease or cancer. And we know that in research, animals¿ calorie restriction reduces the incidence and severity of those age-related maladies, while also delaying their onset. What this shows is that we can now screen pharmaceuticals for finding these effects.¿
Microarray Chips Crystal Ball Quiz
Spindler and his co-authors ¿looked at 11,000 genes, and were able to compare their expression in young, old and very old female mice that had been either calorie-restricted or normally fed. Okay, ladies,¿ we told them, the party¿s over.¿ All their lives those animals were able to eat almost as much as they wanted. We didn¿t let them get fat; just allowed them to eat a normal diet. Then we switched them for exactly four weeks from that normal regimen to a calorie-restricted diet.
¿Next,¿ Spindler went on, ¿we compared the expression profiles of those 11,000 genes to see how the dietary groups differed. They represent about one-third of the 30,000 genes in the murine genome. We queried that gene-chip array: What gene level do you express in the liver in a normally fed mouse? A young calorie-restricted mouse? A normally fed CR mouse that¿s old? And a very old mouse that¿s been switched from one diet to another?¿ ¿Of the 11,000 interrogated genes, 46 replied ¿ how they changed expression during aging in the liver. Twenty went up, 26 went down. What those told us,¿ Spindler said, ¿was that those genes had changed in a normally fed animal with age.¿
He explained why the group chose the liver as ¿an intriguing target: One, liver detoxifies much of what we eat. Our food is absorbed through the intestines into the blood, including a lot of toxins. All that gets absorbed and goes to the liver for detoxifying.
¿The other tissues that investigators have looked at up to this point,¿ Spindler noted, ¿post-mitotic cells like muscle and brain, were incapable of dividing. So we presumed that the mitotic tissue of the liver, which is thought to age well from a clinical perspective, would be very interesting to look at ¿ and indeed it was. We learned a lot about the effects of calorie restriction on cell cycling, apoptosis and genes.
¿Two other things,¿ Spindler pointed out: ¿The liver controls blood glucose. And CR lowers blood glucose and reduces insulin levels. Also, the liver directs the composition of the blood, and thereby controls cardiovascular health. We decided that all of those things made the liver an interesting organ to study.
¿The kind of changes we saw in the liver,¿ Spindler recounted, ¿was that in the animals¿ cells there was an increase of genes implicated in inflammatory response and stress response. We knew that that¿s bad, because inflammation and physiological stresses lead to cancers. We also saw a loss in the expression of genes in the liver that are important for detoxifying chemicals that we absorb from our environment directly in our diet.
¿We saw a loss as well in the ability of the liver to make precancerous cells commit suicide ¿ apoptosis. And one other thing that the liver loses with age is the facility of dividing and regenerating itself.¿
Human Trials Now Under Way
Extrapolating from mice to the human condition, Spindler allowed, ¿is uncertain at present for the simple reason that it hasn¿t been proven yet that calorie restriction works in people. But in my opinion, the vast bulk of the data support the idea that it will. We know that the number of age-related diseases, like cancer and heart disease, increase with increased eating, increased weight.
¿We are doing clinical studies right now,¿ he said. ¿I can¿t go into detail, but they won¿t be like a Phase I or Phase II drug trial. It¿s a protocol where we¿re laying the groundwork for being able to do pharmaceutical studies in humans. But we first have to know what the effects of calorie restriction ¿ long term and short term ¿ are on the gene expression profiles of people.¿
The university has received an allowance on a pending patent application covering in vivo experimental results and methodology, as reported in PNAS. It presumably will be licensed to LifeSpan Genetics. Corp., a drug-screening firm in San Jose, Calif., co-founded last year by Spindler, the company¿s chief scientific officer. ¿We are in late stages of arranging to begin testing for several clients,¿ he concluded.