Dr. Hayflick of ULCA in 1961, postulated the theory for ageing, which has been finally, scientifically proven and accordingly the fundamental cause of ageing is cells’ limited replicative potential. His scientific experiments established conclusively that mortal cells divide up to a hundred times or so. This limited capacity is referred to as the “Hayflick Limit”.
Professor Hipkiss says:
Ageing may be inevitable in complex organisms; indeed it is surprising that we live so long given the multiplicity of insults to which our cells are continuously subjected. Only homeostatic mechanisms (self-repairing, self-balancing, including antioxidant functions) enable our survival. Maybe, if we wish either to live longer or to resist the ravages of time, we should design further homoeostatic systems to repair our repair systems.
Doctors Cranton and Frackelton dramatically underline the importance of dealing with free radicals:
When free radicals in living tissues exceed safe levels, the result is cell destruction, malignant mutation, tumor growth, damage to enzymes and inflammations, which manifest clinically as age-related, chronic degenerative diseases. Each uncontrolled free radical has the potential to multiply a million-fold. But, when functioning properly, our antioxidant systems suppress excessive free radical reactions.
Ageing has been defined as the ‘sum total of all changes that occur in living organisms with passage of time that lead to functional impairment, increased pathology and death’. A general decline in various biochemical and physiological functions in most of the organs ocurs during ageing and this increases the susceptibility of individual to age-associated diseases.
Discussion on Theories of Ageing –
Senescence can be defined as intrinsic adverse changes during ageing of an organism. This is a manifest as an increasing likelihood of death as a function of time, measured from birth or from some developmental stage. Cell senescence refers to the limited proliferative capacity of cultured somatic cells.
There are various theories put forward to explain the process of ageing. These are –
Disposable Soma Theory – The optimal allocation of energy for an organism is done in such a way that energy invested in somatic maintenance is just enough to ensure reproduction. Human being consumes 40% of energy in brain activity, and about 30% energy in maintaining of transmembrane potentials (from which many cellular processes are driven) and to maintain body temperature. Thus energy conservation is not a significant selective advantage to humans and mammals.
Somatic Mutation Hypothesis – DNA is inherently unstable and is susceptible to numerous modifications and damaging agents. Genetic material requires constant maintenance. It was thought that ageing process may be due to accumulations of somatic mutations throughout the lifespan (which are responsible for dysfunction of cells and consequently of organs and individuals). But since DNA damage is fairly random, while ageing is largely consistent over the population, this theory is not acceptable.
Mitochondrial DNA damage – Reactive oxygen species are produced by mitochondria in oxidative phosphorylation, the biochemical pathway by which oxygen is used to produce energy. Human mitochondrial DNA is 16.6 kb and encodes genes for peptides for oxidative phosphorylation and for rRNA and tRNAs required for translation of these genes. It has been proposed that accumulated mitochondrial DNA damage is a mechanism in ageing. Mitochondria with genomic deletions are enriched due to replicative advantage. It is then not understood as to how do babies which are born young escape getting mother’s 20-40 year old mitochondria.
Cell Senescence – Various human cells when cultured in a dish or flask are found to undergo less than about 100 divisions, at which point the cells adopt a distinctive appearance and do not divide further. Here it is argued that senescence in tissue culture is an artifact due to improper or inadequate signalling or an adaptive tolerance to signals. The situation is confusing because there is inverse correlation observed between number of divisions obtained and age of donor and correlation exists also between species lifespan and number of divisions obtained. Cells from a patient of Werner’s syndrome (premature ageing) have reduced proliferative capacity. Cell senescence occurs in vivo and may be responsible for loss of homeostasis in tissues of elderly. Tumor cells do not senesce in culture and it is thought that senescence occurs as a tumor-control mechanism by providing an additional hurdle for growth-errant cells. There is no direct evidence obtained for cell senescence in vivo.
Genetic damage as cause of ageing – Since it is found by experiments (cell fusions between young and senescent and complementation studies), that senescence is a dominant property, DNA damage can not be responsible for ageing. Immortality can not be due to retaining of a function, which is lost by senescent cells, or gaining of a function because this would have resulted into immortality being dominant. Senescence can not be due to gain of function mutation simultaneously in all senescent cells. Immortality may be due to a loss of function which wild-type retains is another possibility.
Telomere shortening – Human telomeres get shorter on average as a function of age. They are elongated in sperms and are shorter in cells that senesce. It was proposed that telomere shortening may be responsible for cell senescence and is involved in ageing process. But no causal role is proved in this theory. Evidence against theory of telomere shortening being responsible for ageing is that : Telomere shortening in yeast leads to death not the phenotype seen in mammalian cell senescence; Also mouse telomeres are upto 10 times as long as that in human cells and yet mouse cells senesce faster.
Oxidative stress hypothesis – Modifications and damage to cellular molecules by free radicals is capable of altering “genetic programmes” and disrupting cell function, thereby contributing to ageing regardless of DNA damage. There is an extensive work on such role of free radicals causing damage to DNA, proteins and lipids. Also there is clear correlation between lifespan and oxygen consumption / body weight in number of species. Enzymes (SOD, catalase, glutathione peroxidase) involved in free radical metabolism are known, though their regulation is not well understood.
Theory of DNA methylation – Methylation of cytidine residues of DNA has been correlated with gene expression levels in number of cases. However, it is not understood as to whether methylation is a cause or result of altered chromatin structure. DNA methylation is thought to be responsible for imprinting and may have a role in mechanism of development and ‘ageing’. In mice DNA methylation level decreases from age of 6 months to 24 months and thereafter it increases.
Ageing and ageing related diseases – 85% of the ageing population succumbs to one of seven ailments – atherosclerosis, hypertension, adult-onset diabetes, obesity, Alzheimer’s and other ailments, cancer and decreased resistance to infections. A number of hereditary disorders result into short lifespans during which the senescence process is apparently accelerated. Though there is no exact match there is striking similarity in wild-type ageing phenotype and such hereditary disorder cases. Genes causing these syndromes may be significant in regulating ageing process.
Theory of calorie restriction – It was observed in 1930s that rats which were fed less but supplied proper nutrition lived longer. Metabolic rate was thought to serve as “genetic clock”. Large number of physiological and pathological symptoms of ageing are delayed in calorie restricted animals. The onset of tumors, which kill about 50% of all mice, is delayed in calorie restricted mice. However there is no direct evidence for hypothesis of effects of calorie restriction on ageing.
Though there are many theories that have been put forward to explain the process of ageing, none of them give a complete satisfactory explanation of all that is responsible for ageing. Most of the observations look like symptoms of ageing rather than causes of ageing or may be, partly a cause of ageing.
We will see more information on research related to some of these observations.
- Ageing and research in genetics
- Telomere and Ageing
- Ageing and Mitochondria
- Ageing and Free radicals
- Ageing and Dietary Restrictions
- Ageing and DHEA
- Ageing and Ageing-associated Diseases
- Ageing and Transplantation
- Measuring ageing quantitatively by simple blood test
Ageing and research in genetics –
Bertram MJ et al have reported in Molecular Cell Biology of Feb. 1999, the identification of a gene that reverses the immortal phenotype of a subset of cells and is a member of a novel family of transcription factor-like genes.
Based on the dominance of cellular senescence over immortality, immortal human cell lines have been assigned to four complementation groups for indefinite division. Human chromosomes carrying senescence genes have been identified, including chromosome 4. The cloning and identification of a gene, mortality factor 4 (MORF 4), which induces a senescent-like phenotype in immortal cell lines assigned to complementation group B with concomitant changes in two markers for senescence, is reported. MORF 4 is a member of a novel family of genes with transcription factor-like motifs. The sequences of the seven family members, their chromosomal locations, and a partial characterization of the three members that are expressed is presented. Elucidation of the mechanism of action of these genes should enhance our understanding of growth regulation and cellular ageing.
Structure and function of Senescence Marker Protein (SMP-30) and its gene has been identified and described. SMP-30 shows androgen-independent decrease in the livers of ageing rats. Gene for SMP-30 is found in mice, rat, human but is absent in yeast.
Telomere and Ageing –
Telomeres are distinct ends of chromosomes. They can be seen under light microscope. They provide non-sticky ends to chromosomes, so chromosomes can not fuse end to end. Length of telomere indicates age or number of divisions that cell has gone through. Replication fork advances as DNA duplex unwinds. Leading strand reaches upto telomere. Lagging strand is short by, equivalent to length of RNA primer (i.e. 10 basepairs). Therefore unpaired portion of strand is subject to nuclease degradation. In each round of replication telomere is progressively whittled away. In normal cell telomere shortens with each division. Eventually it becomes so small, that cell can not divide. Telomere acts like a molecular clock that controls ageing.
Telomeres are the protein-DNA structures at the ends of eukaryotic chromosomes. In yeast, and probably most other eukaryotes, telomeres are essential. They allow the cell to distinguish intact from broken chromosomes, protect chromosomes from degradation, and are substrates for novel replication mechanisms. Telomeres are usually replicated by telomerase, a telomere-specific reverse transcriptase. Also telomerase-independent mechanisms of telomere maintenance exist. Telomere replication is both cell cycle- and developmentally regulated, and its control is likely to be complex. Because telomere loss causes the kinds of chromosomal changes associated with cancer and aging, an understanding of telomere biology has medical relevance. There is an evidence to suggest that, in higher organisms they normally play a role in controlling cell aging.
Telomerase enzyme is RNA sequence plus protein. It is terminal deoxynucleotidyl transferase. It adds TTAGGG repeats at 3’end. It acts as a template for addition of further bases. It balances lost portion. It maintains full length of telomere. Telomerase enzyme is inactive in somatic cells. Ageing or senescence is related to action of telomerase enzyme. In essence, the presence of telomerase in cells ensures the constant, regular and continual resynthesis of telomeres’ repeated sequences of (TTAGGG) – (the code for the cap) placed at the end of telomeres that prevents their endings from unwinding.
Telomerase is unusual because it includes an RNA, which serves as a template for telomere synthesis, in addition to the protein that actually accomplishes the synthesis. Cell biologists had been able to isolate only the RNA, and only from protozoa, yeast, mouse and human. Telomerase protein has been isolated from protozoa and yeast. Abnormal activation of telomerase may contribute to cancer development, hence cancer researchers are interested in the study of these newly revealed molecules as potential targets of chemotherapy.
Telomerase enzyme blocks a process that limits lifetime of most of the cells. It acts on telomere. Cancerous cells make telomerase enzyme. This enzyme permits telomere to maintain its length. Therefore unlimited division is possible in cancerous cells. Protein, which is essential part of telomerase enzyme is discovered. This protein will serve as target for drugs. Testing of drug to inhibit its action can be studied. Drug that blocks action of telomerase, i.e. telomerase inhibitors will be effective on cancerous cells.
Scientific experiments have shown that in cancer cells, telomerase is constant and is produced at optimal levels, and has different set of characteristics than that from the mortal cells. These types of cells had unlimited replicative capacities and their telomeres never shortened. Correlation between telomerase expression and failure to undergo replicative senescence may be useful for considering telomerase activity as a diagnostic and prognostic tool in cancer.
Cancer cells, which have very long telomeres too, do not age and possess the same capabilities thus ensuring that a complete data bank of genetic information is passed on from generation to generation. The present telomerase enzyme had clearly left its mark by imparting immortality upon them while ensuring telomere’s positioning within the strict limits of established coordinates and that their endings are well capped.
The types of cells such as hematopoietic and more specifically, blood, gastrointestinal and skin cells, which do age with time, have the seldom expressed gene of telomerase producing inadequate levels of telomerase., This effectively limits their ability to replicate and thus by virtue of genetic programming, the latter ultimately predetermine their finite span of life.
The telomerase is indeed the chemical agent promoting cells’ longevity and vitality. The gene for telomerase has been dubbed as the “agent of life”. It has also earned itself the title as the “Ambrosia of Life”.
In experiments with mortal cells it has been proven that when reintroduced and activated successfully, the telomerase lengthened the telomere strips, the cellular clocks, and when inactivated the latter gradually shortened and after becoming senescence withered and died out. Thus, to introduce telomerase in mortal cells is to rewind the clock of aging, to restore cells’ vitality and instantly transmute them from mortal to immortal. This permanently imparts upon them the ability to indefinitely proliferate, perpetual flow of high energy – the very life itself. Telomerase may be used to grow back the telomeres and thereby to extend life of human cells.
Youthful appearance, vigour, freedom from age-related illnesses can be expected from if we can stop the cells from ageing and in turn regulate the whole physiology of the system towards immortality.
Geron is the leading biotechnology company which has focused on human aging. Its mission is to develop novel therapeutics for the many manifestations of aging through breakthroughs in the basic genetic mechanism of cell aging and immortalization. The Company’s technology is largely centered around the genetic clock of cell aging – the telomere, and the key that is believed to rewind the clock of cell aging – telomerase. The Company’s proprietary technology platform has many applications in medicine from age-related diseases to cancer.
Ageing and Mitochondria –
There is a clock that is ticking away in every living being – for a dog for 10 years, for a turtle for 150 years, for a mouse for 3 years and for human being 70 odd years. This clock is probably metabolic rate of animal, i.e. the rate at which animal burns its fuel (food). Metabolism produces free radicals More metabolism and more free radicals. Reduce the calories by 40% and increase the life by 40%.
Mitochondria are the first to be damaged by free radicals and when mitochondria are damaged free radical formation worsens. This results in less energy and degenerating tissues. This further leads to ageing and ageing related diseases. Genes, proteins and lipids are vulnerable targets for free radicals. Cancers result when key control genes are hit, heart diseases result when attack is on low density lipids, and wrinkling results when attack of free radicals is on collagen proteins. (Antioxidants are produced naturally and are found to be more in young than in old.)
Birds are interesting exceptions to these metabolic rates’ effects. They have the same metabolic rate and size as that of rat. But pigeon lives 30 years as compared to 4 years of rat. A bird has 5-7 times metabolic potential of non-primate mammals. Their mitochondria are extremely robust to attack of free radicals from metabolic fallout. Mitochondria of long-lived species are constructed differently and produce less free radicals.
Ageing and Free radicals –
Evolutionary theory predicts substantial interspecific and intraspecific differences in the proximal mechanisms of ageing. Search is on for common (‘public’) mechanisms among diverse organisms amenable to genetic analysis. Oxidative damage is a candidate for such a public mechanism of ageing. Long-lived strains are relatively resistant to different environmental stresses. The extent to which these stresses produce oxidative damage remains to be established.
Scientists increasingly believe that free radicals play a major role in causing many ailments and in ageing. By reducing cellular damage caused by free radicals we effectively increase our resistance, strengthen our immune system, and slow down the ageing process. The scientists’ study involved toxic chemicals called free radicals, which destroy cells in the body. They found that free radicals, are normally destroyed by an enzyme called superoxide dismutase (SOD), whose effectiveness diminishes as the body gets older.
Oxidation is the corrosive process that takes place both inside and outside of the body. It is similar to the rusting of metal, or turning brown of peeled apples, and meat going off or fats going rancid. Oxidation is also supposed to be responsible for skin wrinkling. Free radicals are by-products of cellular activity that can damage other cells or cause undue stress on the body. Antioxidants neutralise them before they can exert any harmful effects. Athletes or persons engaged in intense / prolonged exercise need higher level of antioxidants than others. After exercise production of free radicals is high. Free radicals are also produced in our body by environmental insults – from toxic substances, which we breathe, smoke, eat or touch. Cells in our immune system however purposely make free radicals and use them to kill bacteria and viruses.
Damaging effects of free radicals –
- damage to cells occurs,
- protein synthesis becomes impaired,
- proteins become cross-linked and tangled,
- tissues become less pliable,
- arteries incur damage leading to atherosclerosis,
- genetic material (DNA/RNA) is damaged leading to possible cancer development and to inefficient repair processes,
- age pigments accumulate which literally drown the cells in lipofuscin, preventing them from functioning, and
- in general all the signs and indications of ageing are promoted, whether this is stiffness, poor circulation or wrinkles (cross-linkage), not to mention diseases such as atherosclerosis, arthritis, cancer and, it is now believed, Alzheimer’s disease,
- responsible for the damage which occurs in cataracts due to cross-linkage of proteins, :
- Oxygen free radicals can also damage DNA, which if it is not repaired, could give rise to altered, mutant proteins.
- Free radicals degrade tissue strengthening collagen within the bodies’ joints, skin and organs.
Free radicals are implicated in more than 80 diseases, ageing, inflamation of joints and other tissues, Improper functioning of circulatory, nervous and immune systems. Arthritis, Rheumatism, Cancer, Heart problems, Parkinson’s disease, Asthama, Diabetes, Alzheimer’s disease, Stress etc. are disorders in which role of free radicals is implicated.
This destructive process of oxidation is the result of the work of free radicals in the body. We have natural defenses (enzymes) against free radicals but they may get overwhelmed. Therefore antioxidants in nutrition can come to the rescue. ‘Pycnogenol’ is extract of bark of French Maritime Pine. It contains powerful antioxidants – Proanthocyanidines. A natural combatant of that process is to be found in grape skin and seed extract (proanthocyanidins) – a major ingredient contained in Alenol which offers protection for the health of our entire circulatory system.
Alenol contains grape seed extract which provides a rich source of the nutrient that inhibits free-radicals and the destructive process of oxidation which takes place in the human body and results in the ageing process. Alenol wages war on wrinkles.
Scientists are a step nearer to developing a drug, which could extend the average lifespan to 120.
The Canadian scientists (John Phillips, professor of molecular biology at Guelph University in Canada) have found a way of postponing the natural ageing process and increasing life expectancy by up to 40 per cent. The group was investigating the ageing process of fruit flies when it made the discovery. Researchers believe that the finding will give clues into how our bodies break down and die.
When an improved version of the gene for superoxide dismutase was given to fruit flies they lived up to 40 per cent longer. Years of research will be needed before the technique can be tried out on humans. Gene Therapy on flies in Raj Sohel’s laboratory, giving extra genes for SOD (superoxide dismutase) and catalase showed extra 1/3 life than control.
Ageing and Dietary Restrictions –
Superoxide dismutase, glutathione peroxidase are most potent free radical fighters, when restricted diets are followed. Marked lessening of catalase activity in organs like liver and kidneys is one of the signs of ageing. Dietary restrictions cause 50% improvement in catalase activity as per Weindruch and Walford. Dietary restrictions influence important aspects of body’s ability to cope up with free radicals. Some observations of different studies related to diet and its effects on ageing are –
- Vitamin E deficiency causes premature ageing of red cells in blood. (age specific antigens appear on surface of such red cells and the cells die.) Vitamin E deficiency , in general also causes ageing faster.
- Vitamin E supplementation is found to be associated with less accumulation of lipofuscin (fat-protein substance – age pigment).
- Vitamin E supplementation results into degradation of ozone to form H2O2.
- Vitamin C, vitamin E and coenzyme Q10 are strong antioxidants and their deficiency results into premature ageing.
- Selenium deficiency also is responsible for poor glutathione peroxidase activity in tissues as per study in China.
Taking antioxidants by human being may or may not help to extend life in humans but it has been shown to protect the human being from ageing-related diseases like Alzheimer’s disease.
Ageing constitutes a risk factor for magnesium deficit. Magnesium deficit may participate in the clinical pattern of ageing, particularly in neuromuscular, cardiovascular and renal symptomatologies. The consequences of hyperadrenoglucocorticism- the simplest marker of which is non-response to the dexamethasone suppression test – may include immunosuppression, muscle atrophy, centralization of fat mass, osteoporosis, hyperglycaemia, hyperlipidaemia, atherosclerosis, and disturbances of mood and mental performance through accelerated hippocampal ageing particularly. Magnesium deficit and stress aggravate each other in a true ‘pathogenic vicious circle’, particularly in the stressful state of ageing.
Ageing and DHEA –
DHEA (dehydroepiandrosterone) is present in a nutritional extract from the Mexican Wild Yam. Our bodies convert it into whatever hormones are needed, including estrogens, testosterone, progesterone, or corticosterone. The decline of DHEA in our bodies is directly associated with the physical changes we call “ageing”. Current research also shows benefits from DHEA in cases of Alzheimer’s disease, cancer (especially of the breast), heart disease, obesity and even prostrate problems.
In the past few years researchers have found that Melatonin (of LAMETCO International) possesses unique properties as a free radical neutraliser. LAMETCO’s Melatonin also contains Mexican Wild Yam. It can help relieve the problems associated with PMS and menopause, such as mood swings, hot flushes, osteoporosis, and insomnia. Many antioxidant vitamins and nutrients don’t have the ability to enter cells as easily as does Melatonin. Melatonin has the unique advantage of being able to freely enter all parts of a cell. LAMETCO has also added vitamin A, Beta-Carotene, vitamin E and Vitamin C, to Melatonin making it even more effective as antioxidant.
Ageing and Ageing-associated Diseases –
There are some diseases, which are related to ageing. Cataract, diabetes, arthritis, scleroderma, osteoporosis, atherosclerosis, arteriosclerosis, Alzheimer’s disease, strokes and neurological disorders are some examples. These diseases are rapidly induced in Werner’s syndrome. Ageing-associated diseases are genetically triggered and have underlying mechanisms in common. The discovery of such common pathways may provide targets for the development of drugs to treat one or more of the diseases of ageing. The discovery of ageing-related genes may lead to the development of novel and effective drugs and cosmetic products representing multimillion-dollar markets.
AGENE Research Institute Co., Ltd. is focusing on research of individual ageing and cellular ageing. They are investigating the cloning and the functions of Werner’s syndrome genes and regulatory genes in cell proliferation. These approaches will give the answers about the mechanism directing diseases resulting from ageing. They are going to develop screening system of therapeutic drugs and the assay system of ageing genes expression, which will contribute the development for new therapeutics against ageing associated diseases.
LifeSpan’s gene discovery technology is aimed at identifying disease-associated genes for use as therapeutic or diagnostic targets. The technology is designed to determine gene expression, localization and function, and to provide information to identify the best potential drug targets. Because LifeSpan’s technology is highly flexible, it can be applied to solve a partner’s particular problems within a specific disease area of interest, an approach best described as “customized genomics.” Besides finding new disease-associated genes and drug targets, LifeSpan’s technology can find new cell surface cancer markers and novel secreted diagnostic and therapeutic proteins.
Ageing and Transplantation –
It is observed that transplanted bone marrow cells age faster than normal bone marrow cells. This may have co-relation with the higher incidences of leukaemia and other blood disorders developing later in life of bone marrow recipients.
Telomere shortening may occur, because the donated bone marrow cells must divide many a times to re-build the blood system in transplant recipients. Each time the cell divides the telomere shortens and chromosome becomes unstable and the rate of mutation increases. This may be responsible for higher rate of cancers with the increased life.
By decreasing the pressure on transplanted cells to divide – by transplanting large enough cells or by using selected / modified cells (fewer could be used), there would be less telomere shortening.
According to Lancet Medical Journal’s report, testing of blood, of recipients of bone marrow (age 2 – 14) and their respective donors, clearly showed that recipients had cells with shorter telomeres. The average reduction is equivalent to roughly 15 years of ageing and 40 years in some patients.
Telomere shortening increased the incidences of cancer in long term survivors of bone marrow transplant cases.
Melatonin and ageing –
Melatonin is the hormone secreted by pineal gland. This hormone is related to regulation of many physiological functions like regulation of reproduction, sleep and circadian rhythms in the body. Melatonin is found to have capacity of radical scavenging and as preventive antioxidant. Level of melatonin is observed to be falling with increase in age. Melatonin has direct genomic actions and changes in hormonic level can affect genetic expression. Decline in melatonin concentrations with increase in age, can reduce the activity of ADS genes resulting in decreased concentrations of antioxidative enzymes causing much cellular damage and senescence. There is progressive decline in melatonin secretion with increase in age and is the cause of increased oxidative stress. This is further responsible for cellular damage resulting in senescence and age-associated degenerative diseases. Melatonin is also observed to have capacity to counteract the neuronal damages observed in neuro-degenerative disorders like Parkinsonism and AD which are age-related diseases. This also proves the role of melatonin in the ageing process.
Measuring ageing quantitatively by simple blood test –
Researchers at Beckman Research Institute (California) and Veterinary Administration Medical Centre (St. Louis, Miss.) have conducted physical and cognitive tests and measured the levels of the dozen steroids and peptides in the blood of healthy men aged between 20 to 84. The researchers found that the physical and mental detrioration associated with ageing can be tracked by three measures :
(a) the levels of bioavailable testosterone
(b) the levels of dehydroepiandrosterone sulfate (DHEAS) and
(c) the ratio of insulin like growth factor 1 to growth hormone.
They also believed that thyroid function should be examined as another potentially critical element in the ageing equation. These studies may be useful as first step towards determining biomarkers of male ageing. It is believed that raising the levels of three measures given above in old men reduces some of the symptoms of ageing in them.
- Proc Nat Acad Sci., USA, 94, 7537, (1997).
- Chem. Weekly, Jan. 20, (1998).
- Mol. Cell Biol. 1999 Feb;19(2):1479-85.
- George M. Martin (1), Steven N. Austad (2) & Thomas E. Johnson (3) Genetic analysis of ageing: role of oxidative damage and environmental stresses. Nature – Genetics (May 1996) vol 13 no 1.
- Virginia A. Zakian. Telomeres: Beginning to Understand the End. SCIENCE (December 1995) Volume 270, Number 5242, pp. 1601-1607.
- A time for telomeres. SCIENCE (December 1995) Volume 270, Number 5244, p. 1905 Scientists find new clue to cancer and ageing SOURCE: Reuters [WS] DATE: Monday, January 19, 1998
- Dr. Richard A. Passwater, Ph.D. “The Antioxidant Miracle”… Fights Aging and Disease* The “Super Antioxidant” Army Antioxidants? Oxidants? Free Radicals.
- Elizabeth Finkel as broadcast on ABC’s Ockham’s Razor ‘The Science of Aging’ ‘DNA Science Workshop for VCE Biology Teachers’.
- Bertram MJ, Berube NG, Hang-Swanson X, Ran Q, Leung JK, Bryce S, Spurgers K, Bick RJ, Baldini A, Ning Y, Clark LJ, Parkinson EK, Barrett JC, Smith JR, Pereira-Smith OM, Identification of a gene that reverses the immortal phenotype of a subset of cells and is a member of a novel family of transcription factor-like genes. Mol Cell Biol 1999 Feb;19(2):1479-85.
- Telomerase Expression in Normal Human Cells, Geron Corp. & Uni. Of SouthWestern Med. Centre, Dallhas, in “Nature Genetics”, Jan. 1, 1999.
- Fujita T, Senescence Marker Protein (SMP-30) – Structure & Function, Biochem Biophys Res Commun 1999, Jan. 8, 254(1) 1-4.
- Leon Chaitow, Antioxidants and Ageing, http:// www.healthy.net
- Role of Oxidative Stress in Drosophilla ageing, ‘Expression of Bovine Superoxide Dismutase in Drosophilla augmants resistance to oxidative stress’, Mol Cell Biol. 1991 Feb. 11(2):632-640.
- Gene found which is linked with Alzheimer’s disease, Nature Genetics, Aug. 1, 1998.
- Timothy R. Hughes, Newsgroups: bionet.molbio.ageing, ‘Theories of Ageing’, FAQ organized by Bayer College of Medicine, Houston.
- Venkatramanujan Srinivasan, ‘Melatonin, oxidative stress and ageing’, Current Science, Volume 76, Number 1, 10th Jan 1999, 46-54.
- U. C. Lavania, Seshu Lavania and Y. Vimala, ‘Telomere dynamism and developmental connection of differential telomerase activation in cell proliferation and replicative senescence’, Current Science, Volume 76, Number 4, 25th Feb. 1999, 470-473.