Glycative Stress Research
Online edition : ISSN 2188-3610
Print edition : ISSN 2188-3602
Received : February 6, 2018
Accepted : March 1, 2018
Published online : March 31, 2018

Review article

Glycative stress and anti-aging:
7. Glycative stress and skin aging
Masayuki Yagi, Yoshikazu Yonei
Anti-Aging Medical Research Center and Glycative Stress Research Center, Faculty of Life and Medical Sciences,
Doshisha University, Kyoto, Japan

Abstract

Located on the outermost layer covering a living body, skin is an organ which protects the underlying body from theexternal environment such as shocks, temperature, ultraviolet radiation, chemicals and other threats. Changes to the skin canbe visually recognized immediately and can be a trigger factor of a visual impression of aging such as an uneven skin texture,
wrinkles, a dull aspect, the decline of elasticity and resilience, the loss of firm and supple skin texture and the decline of skinfunctions. Influences of aging due to glycative stress appear in the skin, especially in the protein with a long half-life period,
such as collagen or elastin. Glycation induces the browning reaction of skin proteins and AGEs (advanced glycation end
products) are accumulated. The accumulation of cross-linking AGEs such as pentosidine is a factor of physical damages ofthe formation of disordered protein cross-linking. Thus, glycation of the skin protein affects the maintenance of fiber tissue
stability. Furthermore, the accumulation of CML ( N ε-carboxymethyllysine), which is non-cross-linking AGEs, induces theapoptosis to fibroblast tissues, through the medium of RAGE (Receptor for AGEs). Collagen-CML formation induces the
migration of keratinocyte, which exists on the epidermis, and decreases the adhesiveness to collagen. In addition, diversified
AGEs, which are accumulated in the skin tissues, bind with AGEs receptors to accelerate the secretion of inflammatory
cytokine through an intracellular signal transduction. In this manner, the accumulation of AGEs induces not only physical but
also physiological damages. Skin glycation due to glycative stress affects changes not only on the microlevel but also on themacrolevel so that the changes on the skin are highly likely to be recognized as a visual impression of aging.

KEY WORDS: advanced glycation end products (AGEs), skin aging, appearance

1. Introduction: Structure and function of
the skin

Located on the outermost layer covering a living body,skin is an organ which protects the underling body fromexternal environment such as shocks, temperature, ultraviolet
radiation, chemicals and other threats. The skin is composedof three layers, listing from the outside, which are theepidermis, the dermis, and the subcutaneous fat tissues 1).
The epidermis is the outermost layer of the skin witha thickness of 0.2 mm on average. The epidermis can befurther subdivided into four layers, beginning with theoutermost layer; stratum corneum, granular cell layer,
prickle cell layer and basal cell layer ( Fig. 1 ). The stratum
corneum, which is the outermost layer of the epidermis, has
multifarious functions to repel water, acts as a barrier against
bacterial and viral intrusion, and protects internal organs
such as muscles, nerves, blood vessels and others fromexternal injuries. Therefore, the stratum corneum plays theContact Address: Professor Masayuki Yagi, PhD
Glycative Stress Research Center,
Faculty of Life and Medical Sciences, Doshisha University
1- 3, Tatara Miyakodani, Kyotanabe, Kyoto, 610 - 0394 Japan
Phone/Fax: +81-774 - 65- 6394 E-mail: myagi@mail.doshisha.ac.jp
Co-author: Yonei Y, yyonei@mail.doshisha.ac.jp

most important role to sustain the organism.
Keratinocyte accounts for 95% of the cells that constitutethe epidermis. Epidermal turnover time is the time taken for
the epidermis to replace itself. Keratinocytes are divided andproliferated in the undermost layer, matured, and then migrate
to the surface. Through the cell division in the basal cell
layer, to the division of daughter cells and shedding from thesurface of the epidermis, the turnover time is approximately
40 to 56 days 2, 3).
The stratum corneum, losing their nucleus, constitutes
approximately ten layers of a network and exfoliates
sequentially as scurf. The stratum corneum is composedof keratin and lipids produced by keratinocytes. The
keratinocytes are proliferated in the basal cell layer, produce
keratin, differentiate, mature, and migrate to the upper layer.
Keratin 5 and keratin 14 are formed in the basal cell layer
and keratin 1 and keratin 10 are formed in the prickle cell
layer and the granular cell layer.
Inside the epidermis, the following exists: melanocytes,_ 50 _

Glycative Stress Research 2018; 5 (1): 050 - 0 54(c) Society for Glycative Stress ResearchGlycative Stress Research

Fig. 1. Structures of theskin. 1. Structures of the skin.
Figure
The figure is adapted from adapted from Reference 1).

The figure is adapted from adapted from Ref 1

which are responsible for dark skin color, Langerhans cells,
which are related to the immune function of the skin, andMerkel cells, which are sensory recipient cells.
The dermis tissues with a thickness of 2.0-3.0 mm, arelocated under the epidermis and separated by the epidermis
and the basement membrane. Anatomically the dermis has
a three-layer structure consisting of the papillary layer,
subpapillary layer and the reticular layer. The dermis provides
elasticity and strength to the skin. Substances that composes
the dermis are interstitial components (extracellular matrix),
which compose fibrous tissues, and its productive cells.
The main component of extracellular matrix is collagenfiber (mainly type I collagen and type III collagen). Other
components are elastic fiber (elastin fiber), proteoglycan(hyaluronic acid, chondroitin sulfate and others) and others.
Collagen accounts for 70% of the dry weight of thedermis and provides firmness to the skin. Elastin fiber witha crosslinked structure accounts for 1-2% and provides
elasticity to the skin. Proteoglycan forms colloidal gel
holding abundant water and provides moisture to the skin.
Inside the dermis, sensory nerve endings sense feelings,
comfortability and temperature. Further, the dermis has
hair follicles (folliculus pili), blood vessels and secretory
glands (sweat glands and sebaceous glands), controlling bodytemperature, providing moisture to the skin and maintaining
a resilient condition.
Subcutaneous tissues are a fatty layer with a thickness ofseveral mm located under the dermis. The thickness of thelayer is different, depending on which part of the body it islocated. The functions of the subcutaneous fat tissue are toprotect the body from the heat or the cold of outside air andto absorb a shock as cushioning. Furthermore, it plays therole of energy storage, where fat is stored in adipose cells of
the subcutaneous tissues.

2. Aging in the skin

Changes in the skin can be recognized as visual
information and are associated with the visual impressionof aging. Factors of aging in visual impressions from theviewpoint of beauty are the decline of skin texture, finelines and wrinkles, a dull aspect, the decline of elasticity andresilience, the loss of firm and supple skin texture and thedecline of skin functions.

Perceived age for aging skin appearance

People tend to judge others’ age by physical appearance.
Facial skin appearances could be an influential information
source for perception, such as the conditions of wrinkles,
firmness, sagging, complexion, radiance and texture 4).
Perceived age does not necessarily correspond to chronologicalage. Perceived age could be greatly different from chronologicalage, depending on life environments, life styles, eating habits
and other factors. Especially parts of the body like the face,which is usually visible to others, are easily recognized assigns of aging.

_ 51 _Glycative Stress and Skin Aging

The decline of smooth texture

Area cutanea on the surface of the skin contributes toaging. Sulcus cutis are ridges on the surface of the skin andruns lengthwise and breadthwise extending radially fromfollicles as the center. Crista is surrounded by sulucus cutis
and area cutanea is formed from crista. The skin texture of
the young is smooth and even, and has a structure with aclear and well-ordered concavity and convexity, which forms
a smooth skin texture with the feel that is delicate and dense.
However, the sulcus cutis becomes shallow and unclear
with age, and the follicles become bigger. The cutanea areachanges and the quality of the texture declines in advanced
ages. The skin feels and looks rough and sandy. These
conditions of the skin provide visual impressions of aging.

The increase of wrinkles

Wrinkles show morphological changes on the macrolevel in comparison to the skin texture. Wrinkles begin toappear, around thirty years old, around eyes and mouths andon foreheads and necks 5). Wrinkles increase in number andbecome deeper with aging. The appearances of wrinkles on
the face and neck are related to the movement of muscles
and the exposure to ultraviolet light. Skin tissue fibers areruptured by ultraviolet sun light, lose elasticity and reduce
resilience against deformation.

The increase of dull aspect

The color tone of the skin is determined mainly bymelanin (brown), carotene (yellow) and hemoglobin (red or
blueish red). Further, light reflection and absorption affects
the color tone due to the thickness of stratum corneum or
the condition of the skin surface of texture and wrinkles.
The changes in the tone of the skin accompanied by aging
causes a decrease in redness, an increase in yellowness andthe decline of brightness of color. As a result, the color of theskin looks dark and dull 6). The factors of dullness of the skinare diversified such as pigmentation, the decline of blood
flow, thickened stratum corneum, and glycation, oxidationand carbonylation of skin proteins 7).

The decline of firmness and elasticity

Denatured collagen or elastin in the dermis due toglycation forms a protein cross-linking disorder. As collagenand elastin are associated with firmness and elasticity of theskin, the elasticity and resilience are lost.

The decline of the skin function

The epidermis decreases the proliferation of basal cells
and becomes thin as aging progresses. Then, its turnovertime is prolonged 8). The fibroblast of dermis is reduced inproliferation functions and synthesis capability of matrix
components. Thus, the dermis atrophies and the skin becomeless supple and radiant. One of the factors of reduced
functions of tissues is that hormones and growth factors
have insufficient reaction to skin tissues. The changes ofskin functions induce the delay of barrier function recovery
of stratum corneum, the decline of water retention function(dryness), the changes of the amount of sebum secretion due
to the changes of sex hormone secretion, the decline of skinblood flow, and the changes in the metabolism of lipid andcarbohydrate.

3. Glycation and aging of the skin
The glycation of the skin affects skin aging. Aging,glycation of skin protein due to glycative stress, and theformation of AGEs (advanced glycation end products) induce
the yellowing of skin tone which results in a dark and dull
skin tone.
The proteins of collagen and elastin, which are main
components of the dermis, have a long half-life period andare subject to the influences of glycation 9, 10). Collagen andelastin form a cross-linking fiber in the process of forming
fiber in tissues through lysine and hydroxylysine residue. The
formation of cross-linking AGEs such as pentosidine forms aprotein cross-linking disorder and then stiffens the proteins.
Thus, the glycation of the skin protein influences maintaining
the stability of fiber tissues as factors of physical damage,such as the decline of firmness and elasticity. Further, elastinwith the accumulation of CML (N ε-carboxymethyllysine), a
type of non-cross-linking AGEs, which is difficult to degradeby neutrophil elastase, accelerating aggregation, increasing
fiber diameter, and reducing elasticity and extensibility.
Similarly, protein with an accumulation of AGEs advances
the formation of cross-linking and is difficult to be degradedby protease, prolonging the turnover time of the skin.
In an examination with healthy subjects, face skin tissues
were stained with CML antibody. It was shown that theaccumulation of CML in elastic fibers began between the agesof 30 to before 50. Then, the accumulation of CML expands
over all elastic fibers in the elderly 11). CML are produced in
the skin collagen glycation progresses, which accounts for
33% of collagen during the age of 20’s to 80’s 12). The parts
such as a nose, the middle of the forehead, the chin, and headparietal region parietalis, which are susceptible parts of thesunlight, form more AGEs than the parts such as the chest
region, the back and the thighs, which are less exposed to thesunlight ( Fig. 2 ) 13). Therefore, the glycation of elastic fibers
such as collagen and elastin induce the decline of firmnessand elasticity of the skin.
The exposure to ultraviolet light and oxidative stress ofthe skin promotes the AGE formation 14). Solar elastosis refers
to the condition of the accumulation of aberrant elastin fiber
on the dermis of the parts exposed to sunlight. This disease
is considered to occur, due to the long-term ultraviolet lightexposed skin and the produced AGEs from elastin, which isrelated to wrinkles and hanging folds of loose skin.
Contrarily, the accumulated AGEs in the skin bind with
RAGE (receptor for AGEs,) which exists on the surface ofthe skin, which promotes the secretion of pro-inflammatory
cytokine such as TNF-α, IL-1 and IL-6 through an
intracellular signal transduction 15). Therefore, the formation
and accumulation of AGEs in the skin triggers physiologicaldamages due to these factors. Collagen with the accumulationof CML induces apoptosis of fibroblast through an
intracellular signal transduction 16). In addition, the progressionof glycation in the skin tissues induces CML formation inlysine residue of proteins. Carboxymethyl lysine-collageninduces the migration of keratinocyte, which exists on theepidermis, and decreases the adhesiveness to collagen 17, 18).
The accumulation of AGEs is shown in the epidermis,
which has a shorter turnover time than the dermis. CMLis accumulated in keratin-10 contained in the epidermis 19).
Furthermore, CML also accumulates in the stratum corneumof the outermost layer of the skin. The smooth texture of theskin is reduced in the stratum corneum with abundant CML 20).
The accumulation of CML in the stratum corneum is related_ 52 _Glycative Stress Research

Acknowledgement

to the decline of isotropy of the sulcus cutis and the declineof arithmetic roughness index of the surface of the skin. The
accumulation of CML in the stratum corneum induces thedecline of the smooth texture and causes facial appearance
to look older. In addition, the accumulation of CML in thestratum corneum increases with aging ( Fig. 3 ) 21).
People with a high level of glycative stress look older
than those who don’t. With higher value of fasting blood
glucose level 22) or the abundant accumulation of AGEs 23),
they are recognized to have an older perceived age, even
if they are in a good health, in comparison to people at thesame chronological age without glycative stress.
The glycation of the skin influences changes in the skin,
not only at a micro-level but also at a macro-level and it
contributes to the visual impression of aging.

This work was partially supported by the JapaneseCouncil for Science, Technology and Innovation, SIP (Project
ID 14533567 ), “ Technologies for creating next-generation
agriculture, forestry and fisheries” (funding agency: Biooriented Technology Research Advancement Institution,
NARO).

Conflict of Interest Statement

The authors claim no conflict of interest in this study.

Fig. 2. Expression of advanced glycation end products (AGEs) in normal abdominal human skin.

CML concentration ( μg/μg protein)

AGEs were revealed by immunofluorescence in human skin obtained from a 34-year-old (a) and a 65-year-old (b) woman.
Immunolocalization was carried out on fresh frozen sections using a monoclonal antibody raised against AGEs. Sections
FigureFigure2.
2. Expression
Expression
ofadvanced
advancedglycation
glycation
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endproducts
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ininnormal
normalabdominal
human
skin.
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were
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confocalmicroscopy.
The stainingof AGEs is(AGEs)
very intense(stars) inabdominal
the older skinhuman
comparedwith that
AGEs
AGEs
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bybyimmunofluorescence
immunofluorescence
ininhuman
human
skin
skin
obtained
obtainedfromaa34-year-old
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13).andinyoungerskin.
E, epidermis;D, dermis. Scale bar 50 mm.
The figure
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65-year-old
65-year-old(b)(b)woman.
woman.Immunolocalization
Immunolocalizationwas
wascarried
carriedout
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onfreshfreshfrozen
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againstAGEs.
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werevisualizedvisualizedby
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The
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epidermis;D,D,dermis.
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13.

0.20

0.15

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Fig. 3.
Relationship of CML in thestratum corneum and age.

0.05

Subject: n = 52. y = 0.0012x + 0.0378,
R² = 0.079, p < 0.05. CML,N ε -carboxymethyllysine. The figure isadapted from adapted from Reference 21).

0.00
10

20

30

40

50

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Age (year)_ 53 _

70

80

Glycative Stress and Skin Aging

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