New research explores why there's youth in wine

Spanish explorer Juan Ponce de Leon might have spared himself and his men the travails of their fruitless and ultimately fatal quest for the fountain of youth in the Caribbean in 1513 by staying at home in and quaffing the genuine article from oak barrels in his wine cellar, writes Graeme O'Neill.

At last week's Lorne Cancer Conference, US-based Australian researcher Dr David Sinclair described the extraordinary anti-aging properties of resveratrol, a potent antioxidant in red wine, explaining that resveratrol engages the same geno-protective mechanisms induced by caloric restriction.

Researchers have known for 17 years that a Spartan, low-calorie diet can extend the lifespan of multicellular organisms like nematode worms, mice and fruit flies by 50 per cent or more with minimal loss of vitality. Physically and behaviourally, caloric restriction keeps organisms young and vital, in defiance of their advanced chronological age.

Polyphenolic compounds in the skin of red grapes form resveratrol as wine ages -- it occurs ate relatively low levels in unfermented red grape juice.

Strong evidence points to resveratrol as the chief source of Le French Paradox -- the apparent immunity of southern French populations to heart disease and diabetes, despite a fat-rich diet almost guaranteed to consign the average Westerner to an early grave, with advanced cardiovascular disease and type 2 diabetes.

But according to Sinclair, the health benefits of resveratrol extend beyond its simple powers as an antioxidant. It also prevents cancer and metabolic disorders associated with gene dysregulation, by keeping unstable regions of the chromosomes causing genetic havoc.

Hot biotech

Sinclair heads the Glenn Laboratories for Aging Research at Harvard Medical School in Boston, and is a director and co-founder of Sirtris Pharmaceuticals, which recently made Fortune magazine's list of the world's 25 hottest biotech companies. Sirtris has developed two synthetic derivatives of resveratrol derivatives that are currently in phase I trials in the US. Preclinical evidence indicates they are more potent inducers of anti-aging mechanisms than resveratrol itself. Sinclair showed his Lorne audience a photograph of two mice, one appearing aged, hunched and with a dull, scruffy coat, the other in the prime of health with a smooth, glossy coat. The 'aged' mouse had been fed on a normal diet of mouse chow, and was two years old, the average life span of a mouse. The 'young' mouse, which had been given a 20 per cent lower caloric intake, was three years old -- equivalent to 120-plus years in human terms.

"We're only just beginning to understand, at a molecular level, why this happens," Sinclair said.

On a similar, calorie-restricted diet, rats live 500 days beyond their allotted 1000 days, and remain mentally alert, active, and virtually free of cancer and diabetes. Calorie restriction extends the lifetime of brewer's yeast, from 20 rounds of replication to more than 40.

Sinclair said there is good reason to believe humans could also live up to 50 per cent longer if they were prepared to face the rigours and boredom of calorie restriction -- he tried it himself, and gave up after just two weeks.

Some years ago, Sinclair and a research colleague proposed that genetic instability is the Achilles heel of all living organisms -- and that genetic instability is associated with chromosomal regions containing highly repetitive DNA sequences, up to 200 nose-to-tail repeats, in the case of a ribosomal DNA locus in on chromosome 12.

If these regions become unstable, they are translated into single-stranded RNAs that spontaneously form circlets that remain within the original cell -- they accumulate as the cell undergoes successive rounds of replication, and after 12 divisions, as many as 1000 circularised molecules may clog the cell.

Other chromosomal regions harbour retrotransposons -- mobile genetic elements that can free themselves from chromosomes and disperse through the cell, inserting themselves into genes and disrupting their function by up-regulating, down-regulating or silencing their activity, with potentially catastrophic effects on normal gene networks.

'Striking and scary'

In experiments with yeast, Sinclair and his colleagues identified a gene they dubbed Silent Information Regulator No 2 (Sir2), coding for an enzyme -- a histone deacetylase, actively suppresses such genomic mischief.

When the cell detects a break in a DNA strand, Sir2 moves to the locus and initiates a mechanism that unpacks the DNA around the fracture site, and then repacks it when DNA-repair enzymes have done their job. The re-packing leaves the DNA strand coiled around its histone core protein, but leaves a detectable scar on the chromatin that may become unstable and cause genetic mischief -- including cancer -- later in life. Sinclair described this discovery as "striking and scary".

He said one of Sir2's major functions appears to be suppressing accidental recombination at such unstable loci when cells undergo mitosis. Over-expressing Sir2 in yeast and nematode cells suppresses recombination, and extended normal cellular lifespan in vitro by 30 per cent. Deleting Sir2 gene accelerated the aging process, and caused progressive accumulation of circularised DNA molecules.

In its role as a deacetylase, Sir2 de-acetylates and inactivates other proteins, including oxidised proteins -- protein oxidation and inactivation is also known to be a factor in the aging process.

"What does the yeast model tell us about aging in mammals, when DNA circlets don't exist in mammalian cells?" Sinclair asked. "Maybe it's something to do with the role of epigenetic silencing, genetic instability and aging."

Extended lifespan

He said over-expressed Sir2-like genes in fruit flies and nematode worms extends their lifespan, in the same way as caloric restriction. Deleting the gene prevents the organisms responding to caloric restriction.

The human genome has seven Sir2-like genes, collectively called sirtuins. Their major role, according to Sinclair may be to suppress Line 1 (L1) retrotransposons, which account for 30 per cent of the human genome, and prevent translation of repetitive DNA elements, which account for 20 per cent of the human genome.

The disruptive activity of retrotransposons can disrupt gene activity. So can the activation of repetitive DNA elements, which can trigger major changes in methylation patterns, which regulate which gene turns on where, and when. Cancer and metabolic disturbances are the result.

Cellular stress can inhibit Sir2 activity, unleashing genetic mischief.

Sinclair said resveratrol replicates the role of Sir2, binding and inactivating the same acetylase enzyme targets to maintain genomic stability.

Resveratrol has been shown to extend the lifespan of a tiny African fish, which normally lives about nine weeks, by around 50 per cent. Sinclair said protein inclusions that accumulate in the fish's brain, a marker of aging, are absent in fish that ingest resveratrol.

A resveratrol-enriched diet also shrinks allografted human melanoma tumours in laboratory rats, even though resveratrol reaches only a 200 nanomolar concentration in the bloodstream, so the molecule is very active at low concentrations.

Sir2is known to prevent neurodegeneration, and Sinclair said resveratrol appears to reduce the physical and cognitive symptoms of Huntington's disease, Alzheimer's disease, multiple sclerosis, as well as preventing memory loss, in mouse models of these disorders.

It also flips a metabolic switch in the brain, which causes the body to switch from fat deposition to muscle growth, and results in a conversion of fast-twitch 'sprinting muscle' to slow-twitch 'marathon muscle', as well as maintaining healthy insulin/glucose metabolism to prevent type 2 diabetes.

Sirtris, Sinclair's company, has already raised $45 million in the US for phase II trials for diabetes and two neurodegenerative disorders which will begin before year's end. He said the company may list on the Nasdaq in a year or two, as it approaches phase III trials.