Advanced Glycation End Products

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Advanced Glycation End Products
Andreea Deaconu - andreea.deaconu_at_utoronto.ca Avi
Silver - avi.silver_at_utoronto.ca Hoi-Man Leung -
dorothy.leung_at_utoronto.ca Joshua Smith -
joshd.smith_at_utoronto.ca March 4, 2009
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AGEs An Overview

• Advanced Glycation End Products
• Formed from the reaction of sugar molecule with
  either a protein or lipid molecule without
  enzymatic control
• non-enzymatic glycosylation
• Comes from exogenous sources (ie diet, tobacco
  smoke) and endogenous sources via normal
  metabolism and aging
• High levels of AGEs is implicated in many chronic
  diseases

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Examples of AGEs
Basta, G., Schmidt, A. M., De Caterina, R.
(2004). Advanced glycation end products and
vascular inflammation implications for
accelerated atherosclerosis in diabetes.
Cardiovascular Research, 63, 582-592.
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Exogenous Sources of AGE Diet

• Heating of food can create reactive AGE products
  by accelerating glycation
• Food manufacturers enhance natural flavours by
  incorporating synthetic AGEs into foods
• Foods with significant browning, caramelization
• e.g. donuts

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Exogenous Sources of AGE Diet

• Quantity of AGEs consumed has increased
  significantly in last 50 years
• Direct correlation between serum AGE levels and
  AGE consumed
• Suggesting a relationship between high dietary
  AGE intake and development/progression of
  diabetes-related damage

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AGEs in the Body

• Small proportion of ingested simple sugars
  undergo glycation mainly in the bloodstream
• Intracellular natural sugars (ie
  glyceraldehyde-3-phosphate, fructose) react 10
  times faster than glucose
• Lead to the release of highly oxidizing
  side-products such as hydrogen peroxide
• Half-life of an AGE is double that of an
  erythrocyte

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AGEs in the Body

• Undergo renal clearance at a very slow rate
• Affect nearly every type of cell and molecule in
  the body
• Direct damage to myelin sheath, fibrinogen,
  collagen or endothelial cells
• Indirectly affect body function through
  side-products formed in the reaction leading to
  AGEs

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Receptor of Advanced Glycation End Products
(RAGE)?
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What is RAGE?

• Originally isolated from bovine lung and found to
  be present on endothelial cells, where it
  mediates the binding of AGEs
• A 35-kDa polypeptide transmembrane receptor of
  the immunoglobin superfamily of cell surface
  molecules with a unique NH2-terminal sequence
• RAGE may bind to other ligands aside from AGE.
• Amphoterin
• S110b
• Pattern Recognition Receptor.

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Structure of RAGE

• The receptor consists of 5 domains
• Cytosolic domain responsible for signal
  transduction
• Transmembrane domain anchors the receptor in the
  cell membrane
• Variable domain binds the RAGE ligands
• 2 Constant domains
• There is a short highly charged cytosolic tail of
  43 amino acids, which is necessary for signalling

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RAGE

• Aside from endothelial cells, RAGE may be
  expressed by monocytes/macrophages, neurons and a
  range of other cells whose dysfunction has been
  linked to many chronic disorders
• These include
• Diabetes specifically the vascular complications
• Alzheimers disease
• Inflammation
• Atherosclerosis

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RAGE

• Binding of ligands to RAGE triggers signal
  transduction mechanisms
• including formation of lipid peroxides, and
  activation of NF-?B (a protein complex that acts
  as a transcription factor)?
• Activation of NF-?B leads to subsequent gene
  expression regulated by NF-?B
• Over-expression of NF-?B has been linked to
  cancer, inflammatory and autoimmune diseases
• In addition, ligands of RAGE might induce NF-?B
  co-activators that support and enhance sustained
  NF-?B activation

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Pathways in AGE Formation
Basta, G., Schmidt, A. M., De Caterina, R.
(2004). Advanced glycation end products and
vascular inflammation implications for
accelerated atherosclerosis in diabetes.
Cardiovascular Research, 63, 582-592.
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Pathways in AGE Formation

• Glucose and other reducing sugars react
  nonenzymatically with protein amino groups.
• Leading to formation of Schiff Bases and Amadori
  Products
• Amadori products are highly reactive intermediate
  carbonyl groups that can accumulate or
• React with lysine and arginine functional groups
  on proteins, to form irreversibly bound AGEs.

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Role of AGE in Disease States

• Based on 2 general mechanisms
• Formation of cross-links between key molecules in
  the basement membrane of the extracellular matrix
  (ECM)?
• Interaction of AGEs and the RAGE on cell surfaces
  which alters cellular functions

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Accelerated Atherosclerosis in Diabetes

• Associated with the accumulation of AGEs in the
  ECM and within cells of the vessel wall
• Leading to formation of cross-bridges among
  vessel wall macromolecules resulting arterial
  stiffening and loss of elasticity
• Modifying LDL cholesterol, leading to oxidation
  and plaque formation
• Causing the circulating blood cells to adhere to
  vessel wall

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Accelerated Atherosclerosis in Diabetes

• Associated with RAGE-ligand interaction within
  the vasculature
• Causing the induction of intracellular reactive
  oxygen species (ROS)?
• Linked to the activation of the NAD(P)H-oxidase
  system and and NF-?B
• Leads to transcriptional activation of many genes
  relevant for atherosclerosis such as tumor
  necrosis factors (TNF-a and TNF-h), interleukins
  1, 6 and 8 (IL-1, IL-6 and IL-8), interferon-g
  (IFN-g), and cell adhesion molecules

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Role of AGE in Other Disease States

• Evidence suggests the AGEs are mediators of
  nearly all diabetes complications
• Example Retinopahy
• AGES found in retinal vessels of diabetics
  patients
• Levels of AGEs correlate well with the severity
  of retinopathy present.
• Example Nephropathy
• See characteristic thickening of glomerular
  membrane and accumulation of AGEs
• Results in glomerulosclerosis and fibrosis in the
  kidneys

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Nonpharmacological Therapies

• Dietary Considerations
• Minimize intake of foods high in AGE such as
  meat, cheese, egg yolk
• Decreased cooking temperature
• Broiling and frying can lead to increased amount
  of AGEs

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Pharmacological Therapies

• AGE Inhibitors e.g. Aminoguanidine
• Prevents necessary glycation reactions for
  crosslinking
• Animal studies have shown Aminoguanidine to
  prevent diabetic retinopathy, and nephropathy by
  decreasing AGE accumulation
• But, AGE inhibitors needs to be further studied
  in human clinical trials.

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Pharmacological Therapies

• AGE-breakers
• AGE inhibitors may not be effective in tissues
  with extensive AGE accumulation
• AGE-breakers have been shown to reverse arterial
  stiffening, and disrupt already formed AGE by
  breaking established crosslinks
• e.g. ALT-711, a new thiazolium derivative,
  3-phenyacyl-4,5-dimethylthiazolium chloride

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Pharmacological Therapies

• ALT-711
• Catalytically breaks established AGE crosslinks
  between proteins to
• Reduce arterial stiffening,
• Enhance cardiac output,
• Improve left ventricular diastolic distensibility
  in experimental animals
• Shown to improve arterial compliance and reduces
  arterial pulse pressure in older individuals with
  a stiffened vasculature

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Pharmacological Therapies

• sRAGE Soluble form of RAGE
• Extracellular ligand-binding domain of RAGE
• Blocks AGEs from binding to RAGE
• Suppresses accelerated formation of
  atherosclerotic lesion
• Decreases vascular hyperpermeability
• However, further clinical studies need to be
  done, in order to understand the full scope of
  AGE and RAGE biochemistry and function.

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Summary

• Advanced glycation end products (AGE) are derived
  from the nonenzymatic reaction of reducing sugars
  with free amino groups of proteins, lipids, and
  nucleic acids.
• Schiff Bases and Amadori products are two
  immediates formed.
• Receptor for advanced glycation endproducts
  (RAGE) is responsible for intracellular
  signalling that can disrupt cellular function.
• AGE crosslinkages and AGE-RAGE interaction have
  been implicated in many disease states.
• Many Anti-AGE therapies are being studied
  AGE-inhibitors, AGE-breakers and sRAGE.

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References

• Asif, M., Egan, J., Vasan, S. Lopez, S.
  (2000). An advanced glycation end product
  cross-link breaker can reverse age-related
  increases in myocardial stiffness. Proceedings of
  the National Academy of Sciences of the United
  States of America, 97(6), 2809-2813.
• Basta, G., Schmidt, A. M., De Caterina, R.
  (2004). Advanced glycation end products and
  vascular inflammation implications for
  accelerated atherosclerosis in diabetes.
  Cardiovascular Research, 63, 582-592.
• Bierhaus, A, et al. (2001). Diabetes-Associated
  Sustained Activation of the Transcription Factor
  Nuclear Factor NF-?B. Diabetes, 50(12), 2792-808.
• Goldin, A., Beckman, J. A., Schmidt, A.M.,
  Creager, M. A. (2006). Advanced glycation end
  products sparking the development of diabetic
  vascular injury. Circulation, 114, 597-605.
• Hudson, B.I., et al. (2002). Glycation and
  Diabetes The RAGE Connection. Current Science,
  83(12), 1515-1521.
• Kass, D. A., Shapiro, E. P., Kawaguichi, M.,
  Capriotti, A. R., Scuteri, A., DeGroff, R. C.
  Lakatta, E. G. (2001). Improved arterial
  compliance by a novel advanced glycation
  end-product crosslink breaker. Circulation, 104
  (13), 1464-1470.
• Neeper, M, et al. (1992). Cloning and Expression
  of a Cell Surface Receptor for Advanced
  Glycosylation End Products of Proteins. The
  Journal of Biological Chemistry, 267(21),
  4998-5004.
• Peppa, M., Uribarri, J., Vlassara, H. (2003).
  Glucose, advanced glycation end products, and
  diabetes complications what is new and what
  works. Clinical Diabetes, 21(4), 186-187.