See related article, pages 785–792
Getting Better Without AGE
New Insights Into the Diabetic Heart
David A. Kass
N
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
early a century ago, Maillard first observed that
incubation of glucose with amino acids led to the
formation of a yellow-brown pigment due to nonenzymatic glycosylation.1 This unstable compound known as a
Schiff base can undergo rearrangement over several days to
form the more stable Amadori-type product.2 One wellknown example is hemoglobin A1C, the adduct of glucose
with the N-terminal valine amino group of the ␤-chain of
hemoglobin.3 This process of nonenzymatic protein glycation
differs from enzyme-dependent o-glycosylation, the latter
being a reversible process whereby proteins are modified at
specific residues to effect signal transduction much like
phosphorylation.4,5 Glycated proteins, in contrast, can further
evolve over time, undergoing complex rearrangements to
yield crosslinked proteins known as advanced glycation end
products (AGEs)2,6 (Figure). Importantly, and in contrast to
Amadori product precursors, AGEs are virtually irreversible
once formed. Long-lived structural proteins such as collagen
are particularly vulnerable to AGE crosslinks by nature of
their slow turnover rate.7
AGE crosslinking alters protein biochemistry by reducing
enzymatic activity,8 altering biophysical properties,9,10 and
changing protein interactions with other enzymes. In the case
of collagen, AGE links form throughout the molecule, contrasting to the more limited terminal positions for normal
crosslinking, and this increases its tensile stiffness. In addition, AGE crosslinks render collagen less digestible by
metalloproteinases,11,12 which in turn favors its chronic accumulation in tissue. This can be particularly relevant to
disorders in which collagen synthesis is stimulated by inflammatory cytokines, neurohormones, or mechanical stress. AGE
formation does not require diabetes, although the existence of
elevated sugar increases the likelihood of early less stable
glycation products forming, and so is an important contributor to crosslink formation. However, studies have also shown
that AGE crosslinks develop simply over time, ie, aging
itself.6 These senescent changes play an important role in
disorders such as diverse as Alzheimer’s disease13 and arterial
and myocardial stiffening that contributes prominently to
cardiovascular risks in the elderly.7
AGE also plays an important role in cell signaling, working
by interaction with specific receptors including RAGE, AGER2, and AGE-R3. RAGE signaling has been linked to the
activation of p21(ras), NF-␬B, oxidant radical formation,
proinflammatory cytokines and growth factors (eg,
interleukin-6, tumor necrosis factor-␣, and tissue growth
factor ␤1), and adhesion molecule expression.14,15 Such
signaling is implicated in diabetic glomerular nephropathy
and with endothelial dysfunction and diabetic vasculopathy.
In contrast, AGE-R3 (Galectin-3) may play a protective role,
as mice lacking galactin-3 display accelerated glomerulopathy.16 AGE has been implicated in reducing endothelial cell
function17 and triggering premature senescence in part due to
abnormalities in nitric oxide physiology and the generation of
oxidant species such as peroxinitrite.18 AGE has further been
linked to upregulation of connective tissue growth factor
(CTGF),19 also known as insulin-like growth factor– binding
protein-related protein. CTGF is a potent inducer of extracellular matrix synthesis and angiogenesis, and it is often
increased in tissues of models of diabetes.20
There are a variety of approaches that can block the pathophysiologic effects of AGE. First, AGE and AGE crosslink formation
can be inhibited by compounds such as aminoguanidine (AG),
pyridoxamine, or OPB-9195 [(⫾)-2-iso-propylidenehydrazono-4oxo-thiazolidin-5-ylacetanidide].21 These compounds are designed
to trap carbonyl intermediates to prevent modification of nucleophilic residues in proteins, and are all potent inhibitors of AGE
formation and ultimate AGE crosslinking. Studies using AG were
among the first to demonstrate a role of AGE crosslinks in vascular
stiffening and reduced cardiac diastolic compliance in various
experimental models involving diabetes mellitus or aging. Such
investigations reported that AG treatment enhanced cardiac diastolic
compliance,22 blunted age-dependent decline in arterial distensibility,23 and inhibited CTGF expression and CTGF-dependent matrix
accumulation in diabetic nephropathy.24 In addition to preventing
AGE formation, these agents have been reported to chelate metal
ions at concentrations that are physiologically relevant, so that part
of their effects may be as antioxidants.25
A second method for inhibiting AGE effects is to target
RAGE by infusing a soluble extramembrane portion of the
receptor (sRAGE) to act as a false ligand or using RAGE
antibodies. sRAGE administration has been demonstrated to
improve wound healing in diabetic mice26 and to suppress
early acceleration of atherosclerosis as well as stabilize
established atherosclerosis in diabetic apolipoprotein E–null
mice.27,28 Newer small molecular alternatives to RAGE inhibition are presently under development.
Another approach to inhibiting AGE pathophysiology is
the use of crosslink breaker compounds. These agents contain
a thiazolium structure that can break ␣-carbonyl compounds
The opinions expressed in this editorial are not necessarily those of the
editors or of the American Heart Association.
From the Johns Hopkins University, Baltimore, Md.
Correspondence to David A. Kass, Division of Cardiology, Johns
Hopkins University, Halsted 500, 600 N Wolfe St, Baltimore, MD
21287. E-mail [email protected]
(Circ Res. 2003;92:704-706.)
© 2003 American Heart Association, Inc.
Circulation Research is available at http://www.circresaha.org
DOI: 10.1161/01.RES.0000069362.52165.C9
704
Kass
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
Pathophysiology of advanced glycation end products (AGEs).
Glucose interacts over several hours with reactive amino groups
on proteins to form the unstable and reversible Schiff base.
Over longer periods of time (days), this can further develop into
an Amadori product, a more stable form of protein glycation.
Over periods of months to years, these glycated proteins can
undergo further complex rearrangement to generate AGEs.
AGEs can serve themselves as signaling molecules, interacting
with specific receptors (ie, RAGE), which triggers a broad array
of stress and oxidant response signaling, as well as develop
crosslinks between a given protein that can alter its tertiary
structure and function. This process can be inhibited at several
stages: agents that principally prevent the formation of AGE (ie,
aminoguanidine [AG], pyridoxamine [pyr], and OBP-9195), those
that block AGE interaction with membrane receptors (ie, soluble
RAGE, sRAGE), and crosslink breakers that destabilize the carbonyl crosslink (ie, ALT-711).
by cleaving the carbon-carbon bond between carbonyls.
Among this class, 4,5,-dimethyl-3-phenacylthiozolium chloride (ALT-711) has been the most widely studied. Incubation
of AGE crosslinked collagen with ALT-711 in vitro restores
MMP digestibility of the collagen, a key often used marker of
link-breaker effect. In aged dogs, ALT-711 was shown to
enhance cardiac diastolic compliance in association with an
improvement in net cardiac output due to greater net filling
and stroke volume.29 In nonhuman primates, ALT-711 improved arterial distensibility as reflected by the pulse wave
velocity.30 Effects required several weeks to fully develop
and were sustained for several weeks after drug cessation.
Most recently, ALT-711 has been tested in older human
subjects with basal elevation of arterial pulse pressure and
reduced arterial compliance.31 The drug improved arterial
compliance and lowered pulse pressure compared with placebo control, and importantly, these changes occurred without a disproportionate effect on mean arterial pressure. While
such studies have highlighted the physiological potency and
potential clinical efficacy of this class of drug, there has been
very little assessment to date regarding the impact of ALT711 on AGE-dependent signaling or restoring structural
molecular physiology.
AGE and the Diabetic Heart
705
In the investigation by Candido and colleagues,32 reported
in this issue of Circulation Research, important new insights
regarding the impact of breaking AGE crosslinks on the
diabetic heart are revealed. Using a standard rat model of
diabetes induced by streptozotocin, the investigators treated
animals for 4 months of ALT-711 versus placebo. They
report enhanced collagen solubility, reduced collagen III,
reduced expression of RAGE protein and AGE-R3 mRNA,
and reduced CTGF expression in ALT-711–treated rats compared with diabetic controls. Some of these changes, for
example, the decline in CTGF and RAGE expression, were
observed in nondiabetic control rats treated with ALT-711 as
well, suggesting a mechanism that may not require excessive
accumulation AGE crosslinks. Other changes were observed
only in the diabetic animals.
One important limitation of the study was the absence of
functional analysis to couple with the structural and molecular investigation. The authors did report a significant decline
in brain natriuretic peptide and reduced left ventricular mass
with ALT-711 treatment, and this may well have reflected a
fall in filling stresses associated with improved diastolic
distensibility. However, changes in systolic function as well
as alternative signaling mechanisms may have played a role,
and this important question remains to be answered. Prior
studies have generally shown an association between increased collagen type I and/or I/III ratio with diastolic
chamber stiffening.33 Thus, the physiological consequence of
the ALT-711–induced decline in type III collagen is unclear.
Furthermore, whether changes in cardiac properties were the
direct result of ALT-711 or due in part to reduced systemic
unloading remains unclear. ALT-711 treatment did not diminish arterial systolic pressure in the present study. However, similar findings have been previously reported in dog
and nonhuman primates,29,30 despite a significant decline in
systemic vascular resistance, a result of increased stroke
volume and thus cardiac output. In contrast, the recent human
trial of ALT-711 did not reveal significant effects on vascular
resistance, although diabetic subjects were not specifically
targeted in this study.31. The results for TGF␤1 and ␤ig-h3,
the markers of TGF␤1 activity, were somewhat surprising in
that AGE and AGE-RAGE interaction have been shown to
increase TGF␤1 expression in kidney and vasculature in
various diabetic model studies.34 This may reflect specific
features of the present model and study time points or
differences between cardiac and other end-organ AGERAGE and AGE crosslink signaling. Finally, while enhanced
collagen solubility and amount might be anticipated by a
breaker compound, the mechanisms for alterations in AGE
receptor or CTGF expression are less clear. As noted, similar
declines were observed in normal hearts, suggesting a mechanism that may not entail AGE links.
ALT-711 is presently in advanced phase II clinical trials
that aim to establish dose ranges, test its efficacy for the
treatment of systolic hypertension with and without ventricular hypertrophy, and determine its utility to improve patients
with cardiac failure symptoms despite preserved ejection
fraction. The latter is perhaps most directly relevant to the
study of Candido et al,32 in that reduced diastolic compliance
is thought to play a role in this disorder. The results of these
706
Circulation Research
April 18, 2003
trials are anticipated shortly and should help clarify the
potential that this and future similar agents may play in the
treatment of disorders featuring AGE-dependent stiffening
and altered signaling. In the meantime, the work of Candido
and colleagues and other recent studies supports the contention that unlike fine wine, hearts improve without “AGE.”
Ongoing efforts to block the impact of AGE and AGE
crosslinks may soon offer a novel and important avenue to
enhance cardiovascular health.
References
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
1. Maillard L, Gautier MA. Action des acides amines sur les sucres: formation des melanoidines par voie methodique. C R Seances Acad Sci Ill.
1912;154:66 – 68.
2. Brownlee M, Cerami A, Vlassara H. Advanced glycosylation end products in tissue and the biochemical basis of diabetic complications. N Engl
J Med. 1988;318:1315–1321.
3. Koenig RJ, Peterson CM, Jones RL, Saudek C, Lehrman M, Cerami A.
Correlation of glucose regulation and hemoglobin AIc in diabetes
mellitus. N Engl J Med. 1976;295:417– 420.
4. Iyer SP, Hart GW. Dynamic nuclear and cytoplasmic glycosylation:
enzymes of o-GlcNAc cycling. Biochemistry. 2003;42:2493–2499.
5. Wells L, Vosseller K, Hart GW. Glycosylation of nucleocytoplasmic
proteins: signal transduction and o-GlcNAc. Science. 2001;291:
2376 –2378.
6. Ulrich P, Cerami A. Protein glycation, diabetes, and aging. Recent Prog
Horm Res. 2001;56:1–21.
7. Aronson D. Cross-linking of glycated collagen in the pathogenesis of
arterial and myocardial stiffening of aging and diabetes. J Hypertens.
2003;21:3–12.
8. Facchiano F, Lentini A, Fogliano V, Mancarella S, Rossi C, Facchiano A,
Capogrossi MC. Sugar-induced modification of fibroblast growth factor 2
reduces its angiogenic activity in vivo. Am J Pathol. 2002;161:531–541.
9. Badenhorst D, Maseko M, Tsotetsi OJ, Naidoo A, Brooksbank R, Norton
GR, Woodiwiss AJ. Cross-linking influences the impact of quantitative
changes in myocardial collagen on cardiac stiffness and remodelling in
hypertension in rats. Cardiovasc Res. 2003;57:632– 641.
10. Verzijl N, DeGroot J, Ben ZC, Brau-Benjamin O, Maroudas A, Bank RA,
Mizrahi J, Schalkwijk CG, Thorpe SR, Baynes JW, Bijlsma JW, Lafeber
FP, TeKoppele JM. Crosslinking by advanced glycation end products
increases the stiffness of the collagen network in human articular cartilage: a possible mechanism through which age is a risk factor for
osteoarthritis. Arthritis Rheum. 2002;46:114 –123.
11. Mott JD, Khalifah RG, Nagase H, Shield CF III, Hudson JK, Hudson BG.
Nonenzymatic glycation of type IV collagen and matrix metalloproteinase susceptibility. Kidney Int. 1997;52:1302–1312.
12. Sakata N, Meng J, Jimi S, Takebayashi S. Nonenzymatic glycation and
extractability of collagen in human atherosclerotic plaques. Atherosclerosis. 1995;116:63–75.
13. Picklo MJ, Montine TJ, Amarnath V, Neely MD. Carbonyl toxicology
and Alzheimer’s disease. Toxicol Appl Pharmacol. 2002;184:187–197.
14. Schmidt AM, Yan SD, Yan SF, Stern DM. The multiligand receptor
RAGE as a progression factor amplifying immune and inflammatory
responses. J Clin Invest. 2001;108:949 –955.
15. Heidland A, Sebekova K, Schinzel R. Advanced glycation end products
and the progressive course of renal disease. Am J Kidney Dis. 2001;38:
S100 –S106.
16. Pugliese G, Pricci F, Iacobini C, Leto G, Amadio L, Barsotti P, Frigeri L,
Hsu DK, Vlassara H, Liu FT, Di Mario U. Accelerated diabetic glomerulopathy in galectin-3/AGE receptor 3 knockout mice. FASEB J. 2001;15:
2471–2479.
17. Bucala R, Tracey KJ, Cerami A. Advanced glycosylation products
quench nitric oxide and mediate defective endothelium-dependent vasodilation in experimental diabetes. J Clin Invest. 1991;87:432– 438.
18. Chen J, Brodsky SV, Goligorsky DM, Hampel DJ, Li H, Gross SS,
Goligorsky MS. Glycated collagen I induces premature senescence-like
phenotypic changes in endothelial cells. Circ Res. 2002;90:1290 –1298.
19. Twigg SM, Chen MM, Joly AH, Chakrapani SD, Tsubaki J, Kim HS, Oh
Y, Rosenfeld RG. Advanced glycosylation end products up-regulate connective tissue growth factor (insulin-like growth factor-binding proteinrelated protein 2) in human fibroblasts: a potential mechanism for
expansion of extracellular matrix in diabetes mellitus. Endocrinology.
2001;142:1760 –1769.
20. Way KJ, Isshiki K, Suzuma K, Yokota T, Zvagelsky D, Schoen FJ,
Sandusky GE, Pechous PA, Vlahos CJ, Wakasaki H, King GL.
Expression of connective tissue growth factor is increased in injured
myocardium associated with protein kinase C ␤2 activation and diabetes.
Diabetes. 2002;51:2709 –2718.
21. Mizutani K, Ikeda K, Tsuda K, Yamori Y. Inhibitor for advanced glycation end products formation attenuates hypertension and oxidative
damage in genetic hypertensive rate. J Hypertens. 2002;20:1607–1614.
22. Norton GR, Candy G, Woodiwiss AJ. Aminoguanidine prevents the
decreased myocardial compliance produced by streptozotocin-induced
diabetes mellitus in rats. Circulation. 1996;93:1905–1912.
23. Corman B, Duriez M, Poitevin P, Heudes D, Bruneval P, Tedgui A, Levy
BI. Aminoguanidine prevents age-related arterial stiffening and cardiac
hypertrophy. Proc Natl Acad Sci U S A. 1998;95:1301–1306.
24. Twigg SM, Cao Z, McLennan SV, Burns WC, Brammar G, Forbes JM,
Cooper ME. Renal connective tissue growth factor induction in experimental diabetes is prevented by aminoguanidine. Endocrinology. 2002;
143:4907– 4915.
25. Price DL, Rhett PM, Thorpe SR, Baynes JW. Chelating activity of
advanced glycation end-product inhibitors. J Biol Chem. 2001;276:
48967– 48972.
26. Goova MT, Li J, Kislinger T, Qu W, Lu Y, Bucciarelli LG, Nowygrod S,
Wolf BM, Caliste X, Yan SF, Stern DM, Schmidt AM. Blockade of
receptor for advanced glycation end-products restores effective wound
healing in diabetic mice. Am J Pathol. 2001;159:513–525.
27. Kislinger T, Tanji N, Wendt T, Qu W, Lu Y, Ferran LJ Jr, Taguchi A,
Olson K, Bucciarelli L, Goova M, Hofmann MA, Cataldegirmen G,
D’Agati V, Pischetsrieder M, Stern DM, Schmidt AM. Receptor for
advanced glycation end products mediates inflammation and enhanced
expression of tissue factor in vasculature of diabetic apolipoprotein E-null
mice. Arterioscler Thromb Vasc Biol. 2001;21:905–910.
28. Bucciarelli LG, Wendt T, Qu W, Lu Y, Lalla E, Rong LL, Goova MT,
Moser B, Kislinger T, Lee DC, Kashyap Y, Stern DM, Schmidt AM.
RAGE blockade stabilizes established atherosclerosis in diabetic apolipoprotein E-null mice. Circulation. 2002;106:2827–2835.
29. Asif M, Egan J, Vasan S, Jyothirmayi GN, Masurekar MR, Lopez S,
Williams C, Torres RL, Wagle D, Ulrich P, Cerami A, Brines M, Regan
TJ. An advanced glycation endproduct cross-link breaker can reverse
age-related increases in myocardial stiffness. Proc Natl Acad Sci U S A.
2000;97:2809 –2813 [erratum Proc Natl Acad Sci U S A. 97:5679].
30. Vaitkevicius PV, Lane M, Spurgeon H, Ingram DK, Roth GS, Egan JJ,
Vasan S, Wagle DR, Ulrich P, Brines M, Wuerth JP, Cerami A, Lakatta
EG. A cross-link breaker has sustained effects on arterial and ventricular
properties in older rhesus monkeys. Proc Natl Acad Sci U S A. 2001;98:
1171–1175.
31. Kass DA, Shapiro EP, Kawaguchi M, Capriotti AR, Scuteri A, deGroof
RC, Lakatta EG. Improved arterial compliance by a novel advanced
glycation end-product crosslink breaker. Circulation. 2001;104:
1464 –1470.
32. Candido R, Forbes JM, Thomas MC, Thallas V, Dean RG, Burns WC,
Tikellis C, Ritchie RH, Twigg SM, Cooper ME, Burrell LM. A breaker
of advanced glycation end products attenuates diabetes-induced myocardial structural changes. Circ Res. 2003;92:785–792.
33. Yamamoto K, Masuyama T, Sakata Y, Nishikawa N, Mano T, Yoshida J,
Miwa T, Sugawara M, Yamaguchi Y, Ookawara T, Suzuki K, Hori M.
Myocardial stiffness is determined by ventricular fibrosis, but not by
compensatory or excessive hypertrophy in hypertensive heart. Cardiovasc
Res. 2002;55:76 – 82.
34. Rumble JR, Cooper ME, Soulis T, Cox A, Wu L, Youssef S, Jasik M,
Jerums G, Gilbert RE. Vascular hypertrophy in experimental diabetes:
role of advanced glycation end products. J Clin Invest. 1997;99:
1016 –1027.
KEY WORDS: AGE
䡲
collagen
䡲
diabetes
䡲
RAGE
䡲
heart
Getting Better Without AGE: New Insights Into the Diabetic Heart
David A. Kass
Downloaded from http://circres.ahajournals.org/ by guest on July 31, 2017
Circ Res. 2003;92:704-706
doi: 10.1161/01.RES.0000069362.52165.C9
Circulation Research is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 2003 American Heart Association, Inc. All rights reserved.
Print ISSN: 0009-7330. Online ISSN: 1524-4571
The online version of this article, along with updated information and services, is located on the
World Wide Web at:
http://circres.ahajournals.org/content/92/7/704
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published
in Circulation Research can be obtained via RightsLink, a service of the Copyright Clearance Center, not the
Editorial Office. Once the online version of the published article for which permission is being requested is
located, click Request Permissions in the middle column of the Web page under Services. Further information
about this process is available in the Permissions and Rights Question and Answer document.
Reprints: Information about reprints can be found online at:
http://www.lww.com/reprints
Subscriptions: Information about subscribing to Circulation Research is online at:
http://circres.ahajournals.org//subscriptions/