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Recommended GLYCATION, Advanced glycation end-products, ROS (13) |
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Mailard reaction and cross liking of collagen http://diabetes.diabetesjournals.org/content/43/5/676.short
Diabetes 1994 May; 43(5): 676-683.
Glycation,
Glycoxidation, and Cross-Linking of Collagen by Glucose: Kinetics, Mechanisms,
and Inhibition of Late Stages of the Maillard Reaction Min-Xin Fu, Kevin J Wells-Knecht
The Maillard or
browning reaction between sugar and protein contributes to the increased
chemical modification and cross-linking of long-lived tissue proteins in
diabetes. To evaluate the role of glycation and oxidation in these reactions,
we have studied the effects of oxidative and antioxidative conditions and
various types of inhibitors on the reaction of glucose with rat tail tendon
collagen in phosphate buffer at physiological pH and temperature. The chemical
modifications of collagen that were measured included fructoselysine, the
glycoxidation products Nε-(carboxymethyl)lysine
and pentosidine and
fluorescence. Collagen cross-linking was evaluated by analysis of cyanogen
bromide peptides using sodium dodecyl sulfate-polyacrylamide gel
electrophoresis and by changes in collagen solubilization on treatment with
pepsin or sodium dodecylsulfate. Although glycation was unaffected, formation
of glycoxidation products and cross-linking of collagen were inhibited by
antioxidative conditions. The kinetics of formation of glycoxidation products
proceeded with a short lag phase and were independent of the amount of Amadori
adduct on the protein, suggesting that autoxidative degradation of glucose was
a major contributor to glycoxidation and cross-linking reactions. Chelators,
sulfhydryl compounds, antioxidants, and aminoguanidine also inhibited formation
of glycoxidation products, generation of fluorescence, and cross-linking of
collagen without significant effect on the extent of glycation of the protein.
We conclude that autoxidation of glucose or Amadori compounds on protein plays
a major role in the formation of glycoxidation products and cross-liking of
collagen by glucose in vitro and that chelators, sulfhydryl compounds,
antioxidants, and aminoguanidine act as uncouplers of glycation from subsequent
glycoxidation and cross-linking reactions.
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https://www.jci.org/articles/view/116481 Journal of clinical investigations
June 1 , 1993 DG Dyer, JA Dunn,
et al To investigate the contribution of glycation
and
oxidation reactions to the modification of insoluble collagen in aging and
diabetes, Maillard reaction products were measured in skin collagen from 39
type 1 diabetic patients and 52 nondiabetic control subjects. Compounds studied
included fructoselysine (FL), the initial glycation product, and the
glycoxidation products, N epsilon-(carboxymethyl) lysine (CML) and pentosidine,
formed during later Maillard reactions. Collagen-linked fluorescence was also
studied. In nondiabetic subjects, glycation of collagen (FL content) increased
only 33% between 20 and 85 yr of age. In contrast, CML, pentosidine and
fluorescence increased five-fold, correlating strongly with age. In diabetic
patients, collagen FL was increased threefold compared with nondiabetic
subjects, correlating strongly with glycated hemoglobin but not with age.
Collagen CML, pentosidine and fluorescence were increased up to twofold in
diabetic compared with control patients: this could be explained by the
increase in glycation alone, without invoking increased oxidative stress. There
were strong correlations among CML, pentosidine and fluorescence in both
groups, providing evidence for age-dependent chemical modification of collagen
via the Maillard reaction, and acceleration of this process in diabetes. These
results support the description of diabetes as a disease characterized by
accelerated chemical aging of long-lived tissue proteins. Introduction Glycation (nonenzymatic
glycosylation) is
a nonenzymatic, posttranslational
modification ofprotein, resulting from chemical reactions between glucose
and primary amino groups
(1). The major product in
tissue proteins is fructoselysine (FL),'formed
by glycation of E-amino groups
on lysine residues (Fig. 1). The
extent of glycation of tissue
proteins depends on the ambient glucose
concentration and is relatively constant
with age
(2-4). However, products
formed from FL in subsequent Maillard
or browning
reactions accumulate gradually with advancing age in long-lived
tissue proteins (2-4). These products include N'-(carboxymethyl)lysine (CML) and N'-(carboxymethyl)
hydroxylysine (CMhL), which are
formed by oxidative
cleavage of FL and glycated hydroxylysine respectively (3,
4), pentosidine,
a fluorescent
crosslink formed between arginine
and lysine residues (5-7) (Fig. 1), as
well as unidentified
compounds
with characteristic Maillard-type,
visible wavelength
fluorescence (maxima at Ex = 328
nm,
Em = 378 nm) (4). CML, CMhL, and pentosidine
have
been termed "glycoxidation" products
(4, 8) because
both glycation and free radical oxidation
reactions are
required for their formation from reducing
sugars.
The exact origin of these compounds, i.e., from glucose
vs. ribose
(5), ascorbate
(6, 7, 9), or other sugars (8), is uncertain,
although
present
evidence suggests that they are derived
exclusively from reactions between
proteins and carbohydrates (8). According to the
"glycation hypothesis" of aging and the pathogenesis
of diabetic complications, accumulation of endstage products
of the
Maillard reaction
(also known as advanced glycosylation
end-products
[AGE products]) alters the structural properties of
tissue proteins and reduces their susceptibility to catabolism
( 10, 11 ). These changes
contribute to the aging
of tissues, and when accelerated by
hyperglycemia, to the gradual development of diabetic complications.
Despite the
attractiveness of
this hypothesis, the only
Maillard products known to accumulate
with age, i.e., CML,
CMhL, and pentosidine, result not from
glycation alone: oxidation reactions are
also necessary
for their formation (2-4, 7, 1
1 ). The development of increased fluorescence
of proteins in diabetes and aging is also enhanced
by oxidation reactions, and carbohydrate or lipid-dependent
processes
may also be involved
(8). These considerations
raise questions about the relative importance
of the
glycation and oxidation components of glycoxidation
in the
accumulation of Maillard
products in tissue proteins. To our knowledge,
no
previous studies have made direct comparisons between
the concentrations
and
relative rates of accumulation of the glycoxidation
products CML
and pentosidine in collagen from control and diabetic
populations. There is a similar lack of information on
the relative
contributions of increased glycation vs. increased
oxidation in the accumulation
of these products.
We have attempted
to
address these issues
in the present study,
and show that concentrations of CML
and pentosidine, and Maillard-type
fluorescence, increase in concert in human skin collagen with
age, and that the rate of
their increase is accelerated,
again in
a concerted fashion,
in diabetes. Our data also suggest
that the accelerated
accumulation of glycoxidation products in diabetes
can be
explained
by hyperglycemia and increased
glycation alone, without invoking
an increase in oxidative stress. Our findings support the description
of diabetes as a disease characterized
by accelerated
chemical modification and aging
of collagen via the Maillard
reaction. The relationships
between concentrations
of these biomarkers and the
presence and severity
of complications
in diabetes are considered
in the following article ( 12). Dr. Relman another former editor in chief of the
NEJM said this in 2002
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