BIOCHEMISTRY OF BIOCHEMISTRY OF AGEINGAGEING

DR.MAHENDRA.DR.MAHENDRA.

DEFINITIONDEFINITION

Biological process, which causes increased Biological process, which causes increased susceptibility of organism to disease.susceptibility of organism to disease.

Gradual decline in adaptation of an organism to Gradual decline in adaptation of an organism to its normal environment, following the onset of its normal environment, following the onset of reproductive maturityreproductive maturity

Effects of ageingEffects of ageing

1.Progressive decline in vigor & efficiency 1.Progressive decline in vigor & efficiency of physiologic functions.of physiologic functions.

2.Atrophy of most of the organs.2.Atrophy of most of the organs.

3.Increased vulnerability to infections, 3.Increased vulnerability to infections, trauma & various immune abnormalities.trauma & various immune abnormalities.

4.Increased susceptibility to malignancy.4.Increased susceptibility to malignancy.

Life expectancy and life span.Life expectancy and life span.

Life expectancy: average number of years a Life expectancy: average number of years a body is expected to live.body is expected to live.

Maximum life span: Greatest age reached by Maximum life span: Greatest age reached by any member of that species.any member of that species.

Three stages of problem:Three stages of problem:

1) Biological: Study of molecular, physiological & 1) Biological: Study of molecular, physiological & structural aspect of cell.structural aspect of cell.

2) Clinical: Study and cure of diseases. 2) Clinical: Study and cure of diseases. (Geriatrics.)(Geriatrics.)

3) Sociopsychological: Study of problems of old 3) Sociopsychological: Study of problems of old people. Gerontology)people. Gerontology)

THEORIES OF AGEING THEORIES OF AGEING

1) Programmed Theory.1) Programmed Theory.

2) Error theory.2) Error theory.

1)Programmed Theory1)Programmed Theory

Ageing is result of sequential switching on & off Ageing is result of sequential switching on & off of certain genes.of certain genes.

a) Endocrine theory : acts through hormones to a) Endocrine theory : acts through hormones to control pace of ageing.control pace of ageing.

b) Immunological theory :b) Immunological theory :

A programmed decline in immune functions A programmed decline in immune functions leading to increased vulnerability to infections, leading to increased vulnerability to infections, ageing & death.ageing & death.

Altered responsiveness of immune system Altered responsiveness of immune system with age includes :with age includes :

1) Decreased IL-2 & IL-6 production.1) Decreased IL-2 & IL-6 production.

2)Decreased T cell response to IL-2.& mitogen 2)Decreased T cell response to IL-2.& mitogen stimulation.stimulation.

3) Increased frequency of autoantibody 3) Increased frequency of autoantibody production.production.

4) Decreased antibody response to antigenic 4) Decreased antibody response to antigenic stimulation.stimulation.

Error theoriesError theories

A) A) Wear & tear or age pigment :Wear & tear or age pigment :

• Accumulation of pigment lipofuscin in Accumulation of pigment lipofuscin in cytoplasm of neurons, skeletal & cardiac cytoplasm of neurons, skeletal & cardiac muscles.muscles.

• Pigment is acid insoluble & rich in per oxidation Pigment is acid insoluble & rich in per oxidation products of PUFA.products of PUFA.

Cross-linkingCross-linking

Ageing is due to cross-linking of Ageing is due to cross-linking of macromolecules, nucleic acids & proteins which macromolecules, nucleic acids & proteins which are vital for functions of cell.are vital for functions of cell.

Succinic acid, pyruvate, silicon, lead, Succinic acid, pyruvate, silicon, lead, acetaldehyde, Mn, Ca, Zn are the potential acetaldehyde, Mn, Ca, Zn are the potential cross-linkers.cross-linkers.

Somatic mutationsSomatic mutations

Ageing is due to somatic mutations, which Ageing is due to somatic mutations, which destroys genes & causes loss of chromosomes destroys genes & causes loss of chromosomes of somatic cells.of somatic cells.

These cells do not divide after certain stage of These cells do not divide after certain stage of growth & due to mutations these genes either do growth & due to mutations these genes either do not produce any protein or if they do so ,the not produce any protein or if they do so ,the proteins are defective. proteins are defective.

With age these mutations accumulate & after With age these mutations accumulate & after reaching certain levels inactivate the cell.reaching certain levels inactivate the cell.

Therefore no. of functional cells decreases with Therefore no. of functional cells decreases with age & organism dies when no. of functional cells age & organism dies when no. of functional cells decrease below certain levels. decrease below certain levels.

d) Errors in the proteins :d) Errors in the proteins :Two types of proteins:Two types of proteins:

a) Protein needed for structure (collagen & keratin) & for a) Protein needed for structure (collagen & keratin) & for metabolism (enzymes).metabolism (enzymes).

b) those needed for protein synthesis eg : RNA b) those needed for protein synthesis eg : RNA polymerase, amino acyl t-RNA synthtase.polymerase, amino acyl t-RNA synthtase.

Errors in amino acid sequence of enzymes involved in Errors in amino acid sequence of enzymes involved in metabolism , results in decreased or complete loss of metabolism , results in decreased or complete loss of enzyme activity. enzyme activity.

Change in amino acid sequence of RNA Change in amino acid sequence of RNA polymerase results in synthesis of wrong m-RNA polymerase results in synthesis of wrong m-RNA & proteins.& proteins.

This effect will continue till whole cell is filled with This effect will continue till whole cell is filled with wrong proteins, resulting in deterioration of all wrong proteins, resulting in deterioration of all functions.functions.

Is error the primary cause of ageing or is it Is error the primary cause of ageing or is it secondary effect of primary protein, question still secondary effect of primary protein, question still remained unanswered.remained unanswered.

e) The genetic connection :e) The genetic connection :

Cellular differentiation : Cellular differentiation : Process by which various cells arise from single cell.Process by which various cells arise from single cell.

Due to gene activity these differentiated cells differ in Due to gene activity these differentiated cells differ in capacity to synthesize different proteins.capacity to synthesize different proteins.

The proteins expressed by genes carry out multitude of The proteins expressed by genes carry out multitude of functions & some of the functions are related to ageing.functions & some of the functions are related to ageing.

It is the protein product of these genes which are It is the protein product of these genes which are responsible for longevity or ageingresponsible for longevity or ageing

f) Free radical theory :f) Free radical theory :

First proposed by Denham Harman.First proposed by Denham Harman.

States that damage caused by oxygen States that damage caused by oxygen radical is responsible for many of the radical is responsible for many of the bodily changes that come with ageing.bodily changes that come with ageing.

Free radical have also been implicated in Free radical have also been implicated in degenerative disorders including cancer, degenerative disorders including cancer, atherosclerosis, cataract & atherosclerosis, cataract & neurodegeneration.neurodegeneration.

A Free radical is molecule or molecular species, A Free radical is molecule or molecular species, that contains one or more unpaired electrons & that contains one or more unpaired electrons & is capable of independent existence.is capable of independent existence.

Eg : Superoxide,H2O2, hydroxyl singlet O2, Eg : Superoxide,H2O2, hydroxyl singlet O2,

hydroperoxy radical (HOO-), lipid peroxide hydroperoxy radical (HOO-), lipid peroxide

radical (ROO-) Nitric oxide (NO-) & peroxynitrite radical (ROO-) Nitric oxide (NO-) & peroxynitrite

(ONOO-).(ONOO-).

SOURCES :SOURCES :1)1) Cellular metabolism Cellular metabolism : :

- - Leakage of electrons from ETC.Leakage of electrons from ETC.

- Production of H202 or O2- by oxidase enzyme. - Production of H202 or O2- by oxidase enzyme. Eg. Xanthine oxidase, NADPH oxidase.Eg. Xanthine oxidase, NADPH oxidase.

- Chain reactions of lipid peroxidation.- Chain reactions of lipid peroxidation.

- Peroxisomal generation of 02 ,H202.- Peroxisomal generation of 02 ,H202.

- Production of nitric oxide from arginine.- Production of nitric oxide from arginine.

- During course of phagocytosis.During course of phagocytosis.

- In the oxidation of heme to bile pigments.In the oxidation of heme to bile pigments.

- Autoxidation of Fe+2, Cu+2,Ascorbic acid, Autoxidation of Fe+2, Cu+2,Ascorbic acid, glutathione.glutathione.

- 2) Environmental effects :2) Environmental effects :

- Due to drug metabolism.Due to drug metabolism.- Damage caused by ionising Damage caused by ionising

radiation.radiation.- Photolysis of 02 by light.Photolysis of 02 by light.- Photoexcitation of organic moleculesPhotoexcitation of organic molecules- Cigarette smoke.Cigarette smoke.

Harmful effect of free radicals:Harmful effect of free radicals:

Because of their reactive nature free radical can Because of their reactive nature free radical can provoke inflammation or altered cellular function provoke inflammation or altered cellular function through:through:

1.Lipid peroxidation.1.Lipid peroxidation.

2.Protein modification.2.Protein modification.

3. DNA modification.3. DNA modification.

Lipid peroxidation product:Lipid peroxidation product:

React with amino acid mainly CYS, HIS, LYS to React with amino acid mainly CYS, HIS, LYS to modify protein structure & function.modify protein structure & function.

Can crosslink lipid in cell membrane interrupting Can crosslink lipid in cell membrane interrupting structure & fluidity.structure & fluidity.

Can react with DNA causing mutagenic & Can react with DNA causing mutagenic & carcinogenic effects. carcinogenic effects.

2. Protein modification:2. Protein modification:

- - Proteins are major targets of free radical attack Proteins are major targets of free radical attack because of their high abundance & because because of their high abundance & because they are responsible for most of functional they are responsible for most of functional processes.processes.

- Free radical causes oxidation of sulfhydryl gr. & - Free radical causes oxidation of sulfhydryl gr. & modification of certain amino acid (met, cys, modification of certain amino acid (met, cys, His,try) His,try)

ROS may damage protein by fragmentation, ROS may damage protein by fragmentation, crosslinking, & aggregation.crosslinking, & aggregation.

The net result is that free radical injury may The net result is that free radical injury may result in loss of biological activity of proteins. result in loss of biological activity of proteins.

3. DNA modification :3. DNA modification :

Free radical induced DNA damage includes :Free radical induced DNA damage includes :

- strand break.- strand break.

- DNA- protein crosslink.- DNA- protein crosslink.

- large range of base & sugar modification.- large range of base & sugar modification.

Hydroxyl radical is most prominent in development of base Hydroxyl radical is most prominent in development of base & sugar modification.& sugar modification.

DNA damage also occurs through reactive nitrogen DNA damage also occurs through reactive nitrogen species undergoing mainly nitration & deamination of species undergoing mainly nitration & deamination of purines.purines.

The net result is increased risk of mutagenesis & The net result is increased risk of mutagenesis & carcinogenesis.carcinogenesis.

Oxidative damage is repaired by cellular repair system & Oxidative damage is repaired by cellular repair system &

DNA base damage is by base excision repair.DNA base damage is by base excision repair.

Antioxidants :Antioxidants :

1. 1. Enzymatic : SOD, Catalase, glutathione Enzymatic : SOD, Catalase, glutathione peroxidase & reductase.peroxidase & reductase.

2. Nutrient : B-carotene, A-tocopherol, ascorbate 2. Nutrient : B-carotene, A-tocopherol, ascorbate & selenium.& selenium.

3. Metabolic : glutathione, bilirubin, 3. Metabolic : glutathione, bilirubin, transferrin, ceruloplasmin, uric acid. transferrin, ceruloplasmin, uric acid.

Antioxidants & ageing Gerbils :Antioxidants & ageing Gerbils :

High levels of antioxidants can slow the ageing High levels of antioxidants can slow the ageing process.process.

Study of PBN or N-tert-butyl-alpha-Study of PBN or N-tert-butyl-alpha-phenylnitrone in Gerbils support this hypothesis .phenylnitrone in Gerbils support this hypothesis .

At NIA, Richard Cutler found high levels of SOD At NIA, Richard Cutler found high levels of SOD in longer lived animals.in longer lived animals.

Insertion of extra copies of SOD gene into fruit Insertion of extra copies of SOD gene into fruit flies extend life span by 5 to 10%.flies extend life span by 5 to 10%.

Higher levels of SOD & Catalase seen in long-Higher levels of SOD & Catalase seen in long-lived nematodes.lived nematodes.

Current studies are exploring role of vitamin C & Current studies are exploring role of vitamin C & E in reducing heart diseases.E in reducing heart diseases.

Glucose cross-linking:Glucose cross-linking:

Non-enzymatic glycosylation.Non-enzymatic glycosylation.

Glycation triggers a chain of reactionGlycation triggers a chain of reaction that ends in protein binding together or cross-that ends in protein binding together or cross-

linking, altering their biological roles.linking, altering their biological roles.

AGEs seems to toughen tissues & may cause AGEs seems to toughen tissues & may cause deterioration a/w ageing.deterioration a/w ageing.

AGEs linked to stiffening of connective tissues, AGEs linked to stiffening of connective tissues, hardened arteries, loss of nerve function & less hardened arteries, loss of nerve function & less efficient kidneys. efficient kidneys.

Macrophages:Macrophages:

- - Combat glycation.Combat glycation.

- Macrophages detects AGEs, engulf them & once - Macrophages detects AGEs, engulf them & once broken down the AGEs are dumped into the broken down the AGEs are dumped into the blood steam & are filtered out & eliminated by blood steam & are filtered out & eliminated by kidneys.kidneys.

- Similar to antioxidant, this system is not perfect - Similar to antioxidant, this system is not perfect & AGEs overcome our only defenses against & AGEs overcome our only defenses against them with age.them with age.

Researchers say that, the efficiency of kidneys Researchers say that, the efficiency of kidneys decreases with age & macrophages become decreases with age & macrophages become less active while the levels of AGEs increases. less active while the levels of AGEs increases.

DNA REPAIR : DNA REPAIR :

DNA undergoes continual damage.DNA undergoes continual damage.

Oxygen radicals, UV light,& other agents Oxygen radicals, UV light,& other agents damages DNA in the form of deletions, or damages DNA in the form of deletions, or destroyed sections & mutations, or changes in destroyed sections & mutations, or changes in sequence of DNA bases.sequence of DNA bases.

Repair process may be major factor in ageing, Repair process may be major factor in ageing, health,& longevity.health,& longevity.

DNA damage accumulation leads to DNA damage accumulation leads to malfunctioning genes, proteins, cells.malfunctioning genes, proteins, cells.

Animals ability to repair DNA damage is directly Animals ability to repair DNA damage is directly related to life span of its species .related to life span of its species .

Humans repair DNA more quickly & efficiently.Humans repair DNA more quickly & efficiently.

Most efficient repair seen in sperm & egg cells. Most efficient repair seen in sperm & egg cells.

Photo-ageing damages collagen & elastin.Photo-ageing damages collagen & elastin.

These proteins declines with age.These proteins declines with age.

In ageing process turnover of keratinocytes slows In ageing process turnover of keratinocytes slows down & in photo- ageing, they are damaged.down & in photo- ageing, they are damaged.

Melanocytes decline with ageing & are killed in Melanocytes decline with ageing & are killed in photoageing.photoageing.

Mitochondrial DNA is injured at much greater Mitochondrial DNA is injured at much greater rate than nuclear DNA.rate than nuclear DNA.

Mitochondrial DNA damage increases Mitochondrial DNA damage increases exponentially with age. exponentially with age.

Telomeres :Telomeres :

- - Protects genetic encoding from becoming a Protects genetic encoding from becoming a short sequence during replication.short sequence during replication.

- Tail at the end of every chromosome that gets - Tail at the end of every chromosome that gets shorter as the cell divides.shorter as the cell divides.

-When telomeres become too short their function -When telomeres become too short their function is disrupted & cell stops dividing. is disrupted & cell stops dividing.

Telomerases :Telomerases :

- - Enzyme responsible for restoring lost telomeric Enzyme responsible for restoring lost telomeric sequence in cells. So cell can divide indefinitely.sequence in cells. So cell can divide indefinitely.

- Mostly found in sperm & egg cells. - Mostly found in sperm & egg cells.

Heat shock proteins :Heat shock proteins :

Produced when cells are exposed to various stresses.Produced when cells are exposed to various stresses.

Their expression can be triggered by exposure to toxic Their expression can be triggered by exposure to toxic substances such as heavy metals & chemicals & even substances such as heavy metals & chemicals & even by behavioral & psychological stress.by behavioral & psychological stress.

HSP declines with age.HSP declines with age.

Old animals placed under stress shows lower levels of Old animals placed under stress shows lower levels of HSP-70 than young animalsHSP-70 than young animals

Researchers found a striking decline in HSP-70 Researchers found a striking decline in HSP-70 production as cell approaches senescence.production as cell approaches senescence.

Exact role of HSP – not yet clear.Exact role of HSP – not yet clear.

HSP known to help the cell disassemble & HSP known to help the cell disassemble & dispose of damaged proteins & to facilitates the dispose of damaged proteins & to facilitates the making & transport of new proteins. making & transport of new proteins.

Hormones & research on ageingHormones & research on ageing

1. 1. Estrogen :Estrogen :

- used in HRT to relieve discomfort- used in HRT to relieve discomfort

of menopause.of menopause.

- produced by ovaries- produced by ovaries

- slows the bone thinning process - slows the bone thinning process

2. Growth hormone :2. Growth hormone :

- - Produced by pituitary gland.Produced by pituitary gland.

- Plays a role in body composition & muscle & - Plays a role in body composition & muscle & bone strength.bone strength.

- Released through GHRH.- Released through GHRH.

- Works by stimulating production of IGF.- Works by stimulating production of IGF.

- All three are under study for their potential to - All three are under study for their potential to strengthen muscle & bones. strengthen muscle & bones.

3.Melatonin :3.Melatonin :

- - Produced by pineal gland.Produced by pineal gland.

- Regulates various seasonal changes in body.- Regulates various seasonal changes in body.

- Declines during ageing & trigger - Declines during ageing & trigger

changes in endocrine system. changes in endocrine system.

4. Testosterone :4. Testosterone :

- - Produced by testes.Produced by testes.

- Declines with age.- Declines with age.

- Under investigation for its ability to - Under investigation for its ability to

strengthen muscles & prevent strengthen muscles & prevent

frailty & disability. frailty & disability.

5. DHEA : (Dehydroepiandrosterone).5. DHEA : (Dehydroepiandrosterone).

- - Produced in adrenal gland.Produced in adrenal gland.

- Precursor to testosterone & estrogen.- Precursor to testosterone & estrogen.

-Under study for its effects on ageing-Under study for its effects on ageing

& potential to prevent cancer & multiple sclerosis.& potential to prevent cancer & multiple sclerosis.

Role of dopamine receptors in Role of dopamine receptors in ageingageing

Changes a/w ageing are due to loss of particular Changes a/w ageing are due to loss of particular chemical receptor in the brain.chemical receptor in the brain.

Researchers studied the effect of ageing on Researchers studied the effect of ageing on dopamine, which modulates the communication dopamine, which modulates the communication between areas in brain that are involved with between areas in brain that are involved with movement, cognition, motivation & reward.movement, cognition, motivation & reward.

Investigators measured both the levels of Investigators measured both the levels of dopamine receptors & brain glucose dopamine receptors & brain glucose metabolism.metabolism.

They found that ageing correlated with a loss of They found that ageing correlated with a loss of dopamine receptors & that these losses were dopamine receptors & that these losses were associated with a decline in activity in frontal associated with a decline in activity in frontal region.region.

They concluded that the decline in cognitive They concluded that the decline in cognitive abilities & higher propensity for depression in abilities & higher propensity for depression in elderly is due to losses of brain dopamine elderly is due to losses of brain dopamine receptors.receptors.

Macular degeneration of eye :Macular degeneration of eye :

Normally cornea is transparent & avascular.Normally cornea is transparent & avascular.

Contains chemical –VEGF-A that promotes Contains chemical –VEGF-A that promotes angiogenesis.angiogenesis.

Researcher identified protein VEGFR-1 which Researcher identified protein VEGFR-1 which blocks the blood vessel growth.blocks the blood vessel growth.