Animal life has a curious bargain with oxygen, the gas which is necessary for animal survival but at the same time creates the free radicals that seem to trigger the seeds of cancer.
In recent years it has been recognised that creatures on earth had to adapt to breathe the oxygen produced as a by product of plant life. Oxygen however, as well as sustaining life, also damages cells (just think of rust as an effect of oxidation outside the biological sphere), and a variety of mechanisms have evolved to protect the body.
Oxidation is a normal activity of the cell.
It is an essential process whereby the nutrients we obtain from foods are oxidized in a controlled manner involving the consumption of oxygen. Carried out at a cellular level, oxidation releases energy for metabolism and transformation of nutrients into body tissue and generation of heat. The oxygen is ultimately converted into water and excreted.
However, during this process, so-called free radicals or reactive oxygen species (ROS) are formed that, unless mopped up by the body's antioxidant defences, can damage the tissues, increasing the rate at which they age and potentially contributing to a range of degenerative diseases such as arthritis, immune disorders, cancer, stroke, coronary heart disease, and many others.
Antioxidants are substances produced by the body, or consumed in foods, that significantly delay or prevent the oxidation of a particular substrate.
Scientists discovered a key to aging and lifespan determination.
In Canada, a research team from the University of Toronto working with Dr. John Phillips, professor of Molecular Biology at the University of Guelph, have identified a genetic mechanism that can dramatically delay the ageing process by protecting cells from environmental damage.
They uncovered a critical weakness in the defence against aging. Using the fruit fly as a model biological system, the researchers discovered that a specific cell type, the motor neuron (a nerve cell), is the major target for oxidative damage, known for several years to be a key factor affecting aging and lifespan. The researchers were able to boost the flies' defences by inserting a human gene which is known to protect against oxidative damage. As a result, the average lifespan of the flies (usually about 80 days) was increased by 40 percent.
The study confirms the theory that breathing creates toxic oxygen by-products. These toxins, called free radicals, should be mopped up by the activity of a gene called superoxide dismutase (SOD1). As the body ages, however, the process becomes less reliable and cell damage occurs.
"This research is significant because it clears up a long-standing mystery: which cells, when targeted by oxidative damage, limit the lifespan of the entire organism" says Dr. Boulianne, an associate professor of Molecular and Medical Genetics at Univeristy of Toronto. "In addition, we now know that just one gene, targeting one type of cell, has a huge impact on aging. Contrary to what was previously thought that many different factors contribute to aging it now appears that the process may be simpler."
By inserting the human gene SOD1 (superoxide dismutase) into flies, researchers were able to protect the flies against oxidative damage. This damage, which increases with aging, affects a cell's ability to maintain its structure and function.
"One of life's ironies is that the stuff that we need to survive, oxygen, is actually toxic" explains Dr. Phillips. "When we breathe, toxic byproducts called oxygen radicals are created. Our cells defend against these toxins by either neutralizing or eliminating them. But as we age it becomes more difficult for our cells to cope with the toxins and they accumulate. What we now know is that the nervous system is the most vulnerable to this accumulation because it uses a lot of oxygen."
Motor neurons are cells of the nervous system that form the linkages to muscles. They are highly active, using large quantities of oxygen and producing high levels of waste products.
When the mechanisms for mopping up these free radical waste products break down, the disease process begins.
Other scientist believe that the SOD1 studies will have implications in manipulating the process of conditions like Motor Neurone Disease, which involves damage to neuron cells. These and other genetic manipulations could extend human lives even further.
Oxidative damage has been linked to several human neurodegenerative diseases, including familial Amyotrophic Lateral Sclerosis, Huntington's disease, Parkinson's disease, and Alzheimer's disease.
"This work shows that not only are people going to live longer, but also that they are going to remain healthy for longer" adds Dr. Phillips.
Next, research in the area of oxidative damage to the motor neurons will develop tools to selectively target cells in the nervous systems of humans; more research will identify other types of cells important in the aging process and will determine if there are other beneficial actions that can be taken to affect oxygen metabolism.
A gene called Age-1 which is involved in cell repair was identified by the British scientist Gordon Lithgow, a microbiologist at Manchester University, in another study on ageing. Different mutations of this gene have different levels of repair efficiency. Lithgow is analyzing the blood of centenarians to look for additional genes which control the regeneration of cells.
Some vitamins and trace elements in the diet contribute to the body's antioxidant arsenal. Vitamins A (as beta-carotene), C, and E are known as the antioxidant vitamins, and selenium, copper, manganese, and zinc are components of antioxidant enzymes. In fact the carotenoids, the red-orange pigments in plants, comprise about 600 different substances, of which about 60 are precursors of vitamin A.
Many of the non-provitamin carotenoids, including substances such as lycopene, zeaxanthin, and lutein act as antioxidants. Lycopene is the most interesting of these. It is present in tomatoes and, therefore, in food products such as ketchup and sauces. Cooking releases the lycopene and makes it more available, especially in the presence of a small amount of oil or fat.
Recent epidemiological studies have suggested that consumption of tomatoes and products containing them is associated with a lower incidence of prostate cancer. Consumption of 10 or more servings per week of foods containing tomatoes, including soup, pizza, and pasta sauces, afforded the greatest protection. In addition, non-nutrients such as phytoestrogens, flavonoids, phenolic acids, and polyphenols such as tannins are present in foods and drinks, and may help to prevent oxidation in the plant as well as in human tissues.
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