Download Analysis of glucose levels during glucocorticoid-induced

Analysis of Glucose Levels During Glucocorticoidinduced Cataract Formation in Chick Embryos
Hideo Nishigori, Jung W. Lee, Yasuhisa Yamauchi, Kozuo Maruyama, and Mofoharu Iwatsuru
When 15-day-old developing chick embryos were administered hydrocortisone hemisuccinate sodium
(HC; 0.25 fimol/egg), the content of glucose in the lens markedly increased from around 6 hr, and
reached about 25-30-fold above the matched control at 24-48 hr. Thereafter, the glucose level declined
and returned to the control level by 100 hr. The profile of lenticular glucose levels was similar to that
of the appearance and disappearance of lens opacification. Prednisolne, as well as HC, produced cataract
and the elevation of glucose in the lenses. Cortexolone and cortisone, which have weak or negligible
glucocorticoid activity in developing chick embryo, could neither produce cataract nor the elevation of
glucose in the lenses. An attempt was made to find similarity between this glucocorticoid-induced cataract
and sugar cataract known in mammals. In both control and HC-induced cataract (stage IV-V) obtained
48 hr after HC administration, sorbitol, fructose, and glycosylation of protein could not be detected.
Dehydration was observed in HC-induced cataractous lens. These data demonstrate that the glycosylation
of lenticular protein and the accumulation of polyol were not involved in glucocorticoid-induced cataract
formation in developing chick embryos. These results suggest a relationship between the elevation of
glucose and cataract formation. However, when cataract formation was blocked by ascorbic acid treatment,
the glucose level remained high. Therefore, any relationship between glucose level and cataract may be
complex or indirect. Invest Ophthalmol Vis Sci 28:168-174, 1987
is maintained at a level about 2.5 mg/ml, 8 or by inducing diabetes with drugs.9 The increase in lens glucose in cataract is suggested to be caused by the increase
membrane permeability.
In the present paper, we show that the glucose level
in the lens increased markedly with lens opacification
and decreased with recovery from cataract after hydrocortisone administration. This relationship between
the alteration of glucose level and hydrocortisone-induced cataract formation is discussed in regard to the
hypotheses on the formation of sugar cataract in mammals. 9 ' 11
Previous studies have shown that treatment with hydrocortisone, an adrenocortical hormone, can produce
reversible cataract in developing chick embryos. The
level of glutathione 12 and ascorbic acid3 in the lenses
decreased with cataract formation after hydrocortisone
administration, but returned to the control level with
recovery from cataract. This hydrocortisone-induced
cataract formation was effectively prevented by the administration of radical scavengers, certain SH-compounds, 2 and ascorbic acid.3 These results suggest that
cataract formation by hydrocortisone may be caused
by oxidative attacks produced in ovo.
However, since hydrocortisone is a typical glucocorticoid hormone which causes the alteration of metabolic activities in various tissues,4'5 several other possibilities should be considered for the mechanism of
cataract formation by hydrocortisone. We have focused
on glucocorticoid-produced hyperglycemia in mammals,4 since cataracts are found in a variety of diabetic
animals. For instance, in young rats, sugar cataracts
have been produced by directly feeding galactose or
xylose,6'7 or by a hyperglycemia where the blood glucose
Materials and Methods
One-day-old fertile White Leghorn eggs were purchased from a local hatchery and incubated in a humidified incubator at 37.5°C. To 15-day-old embryos,
hydrocortisone hemisuccinate sodium (HC; 0.25 /xmol
in 0.2 ml sterilized water) as a glucocorticoid was administered through a small hole in the eggshell on the
air sack. '"3 This single dose was based on dosage studies
described previously.1 At the indicated time after HC
administration, the lens and the veinous blood were
obtained from the embryos. Prednisolone hemisuccinate sodium (PS), cortisone hemisuccinate sodium (CS),
and cortexolone hemisuccinate sodium (CX) were also
administered in the same way.
From the Faculty of Pharmaceutical Sciences, Teikyo University,
Sagamiko Kanagawa, Japan.
Submitted for publication: December 3, 1985.
Reprint requests: Dr. H. Nishigori, Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Kanagawa, Japan 199-01.
168
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ELEVATION OF GLUCOSE IN GLUCOCOPJICOID CATARACT / Nishigori er ol.
Determination of Glucose
Determination of Sorbitol
Twenty lenses were sonicated in 0.5 ml of distilled
water and the volume adjusted to 0.7 ml with water.
To this homogenate, 0.7 ml of ice-cold 2 N perchloric
acid was added to deproteinize. After neutralization
with 2 N potassium hydroxide, a centrifugation was
carried out. Whole supernatant was used for the assay
described by Bergmeyer et al.13
Determination of Fructose
Twenty lenses were sonicated in 0.5 ml of distilled
water and the volume adjusted to 0.7 ml with water.
Four percent perchloric acid (0.3 ml) was added to
this. After a centrifugation, the supernatant was assayed
as described by Bernt and Bergmeyer.14
Determination of Glycosylation of Protein
Ten lenses were sonicated in 1 ml of distilled water.
The sample was dialyzed against 100 ml of water to
remove free glucose, and was then subjected to the
colorimetric test of Fluckiger and Winterhalter by using
thiobarbituric acid.15 5-Hydroxymethylfurfural was
used as standard.
Determination of Protein
Protein in lens was determined by the method of
Lowry et al.16
Determination of Glutathione
Glutathione in lens was determined with the use of
Ellman's reagent.17
Hydrocortisone hemisuccinate sodium, prednisolone hemisuccinate sodium, cortisone, and ascorbic
acid were obtained from Sigma Chemical Co. (St.
o
•
Cont. :
HC :
20
moL
E
m
\
3io
ucose
Fifteen lenses were homogenized in 0.7 ml of double
distilled water by a sonicator (Branson Sonic Power
Company, Connecticut) and mixed with 0.3 ml of 4%
perchloric acid. After a centrifugation, 0.1 ml of the
supernatant was used for the determination. Glucose
was determined by an enzymatic method using a kit
of Gluco-Quant (Boehringer Mannheim GmbH,
Mannheim, W. Germany) based on the method described by Bergmeyer et al.12 The amount determined
by this kit shows the sum of glucose and glucosesphosphate. When the actual glucose ("glucose")
amount was required, glucose-6-phosphate, determined
by the method described by Bergmeyer et al,12 was
subtracted. The method of expression, nmol/lens,
closely relates to tissue concentration, since variations
in lens wet weight were small.
&*
o
r\
i
i
03 10
i
•
2024
i
48
T i me ( hr
l
72
l
96
Fig. 1. Blood glucose level in developing chick embryos after HC
administration. HC was administered to 15-day-old chick embryos
(0 hr). Blood was collected at the indicated times after HC administration. Glucose content was determined as described in Materials
and Methods. Data were expressed as mean ± SE (n = 5-30). In the
cases of circles without bars, the bar ranges were smaller than the
diameters.
Louis, MO). Cortisone hemisuccinate sodium and
cortexolone hemisuccinate sodium were prepared from
cortisone and cortexolone (Aldrich Chemical Co.,
Milwaukee, WI).18 Glucose-6-phosphate dehydrogenase, phosphoglucose isomerase, sorbitol dehydrogenase,
ATP-disodium, NADP, and NAD were obtained from
Boehringer Mannheim Yamanouchi Co., Tokyo.
Other chemicals were of analytical grade.
Results
When 15-day-old chick embryos were administered
a single dose of HC, an opaque ring appeared between
the cortical and the nuclear regions in their lenses during the first 24 hr, and the nuclear region became
opaque by 48 hr with a high incidence. By 96 hr after
treatment, the opacity had disappeared.1 During this
treatment period, the blood glucose level was found to
change, increasing to 1.5-2-fold above control between
20 and 72 hr, but returning to control level at 96 hr
(Fig. 1). The elevation of blood glucose was demonstrated to be dependent on the dose of HC. The administration of sodium succinate (0.25 /imol/egg)
which was easily released from HC in ovo only slightly
elevated blood glucose (Table 1). Blood glucosesphosphate could not be detected in either control or
HC-treated animals (not shown).
It has previously been demonstrated that an elevation of blood glucose level induces an increase of glucose in the eye, including the lens of mammals.6"8 Figure 2 shows the profile of glucose levels in the lens after
HC administration. During normal growth of chick
embryos from 15 (0 hr) to 19 (100 hr) days old, the
glucose in the lens remained unchanged at approxi-
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170
Vol. 28
INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE / January 1987
Table 1. Effect of different amounts of HC on blood
glucose of developing chick embryos
%of
Dosage
nmole/egg
mmole/l
7.45 ± 0.43
(33)
100
HC
0.25
0.025
0.0025
15.80 ±0.74
8.57 ±0.51
7.94 ±0.09
(35)
(7)
(7)
212
115
107
Sodium
succinate
0.25
8.60 ±0.22
(7)
115
Control
Number of
embryos
Table 2. The level of glucose-6-phosphate in control
and HC-induced cataractous lens
control
HC at the indicated dosage and 0.25 jimole of sodium succinate were administered to 15-day-old chick embryos, and 48 hr later their blood was collected.
Glucose was determined as described in Materials and Methods. Data were
expressed as mean ± S.E.
mately 2 /umol/lens. When chick embryos were given
HC on day 15, however, the level of glucose in the lens
began to increase prior to the appearance of an opaque
ring; the glucose in the lens began to increase at around
6 hr of HC administration, and reached 25-30-fold
above the matched control between 24 and 48 hr. Interestingly, its level returned to the control level by 100
hr after HC treatment with recovery from cataract.
Glucose in the lenses removed at 48 hr after HC
administration was determined separately as "glucose"
and glucose-6-phosphate (Table 2). The amount of
Control
Glucose-6-phosphate
"Glucose"
Glucose-6-phosphate
HC-treated
Fold
increase
1.95 ±0.53 (4) 2.73 ±0.76 (4)
1.57 ±0.26 (4) 44.34 ±0.13 (4)
1.24
"glucose"
1.4
28.2
0.06
Determination of glucose-6-phosphate: 0.7 ml of twelve lenses sonicated in
water was mixed with 0.3 ml of 4% perchloric acid. After a centrifugation, 0.1
ml of the supernatant was used for assay described by Bergmeyer et al.12 nmol/
lens was calculated. Four experiments were carried out and data were expressed
as mean ± S.E.
"glucose" (1.95 ± 0.53 nmol/lens) and glucosesphosphate (1.57 ± 0.26 nmol/lens) in control lenses
were similar. However, the amount of glucose-6-phosphate after HC administration slightly increased to 1.4fold (2.73 ± 0.76 nmol/lens) at 48 hr, and the levels
were much lower than that of "glucose" (44.34 ±0.13
nmol/lens).
The effects of PS, CS, and CX on cataract formation
and glucose level in lens were determined (Table 3).
At the same time, glutathione level in lens was also
determined. PS (0.25 /^mol/egg), as well as HC, produced cataract formation, the elevation of glucose, and
the decline of glutathione in the lens. However, when
0.25 /Limol/egg of CS or CX was administered, little
effect on cataract formation, the elevation of glucose,
and the decrease of glutathione could be observed. One
Table 3. Relationship between steroid structure
and cataractogenesis
Lens
Dosage
Frequency of
cataract
nmole
per egg
o
II
0
III
0
IV-V
0
0.025
0.25
30
2
6
0
0
2
0.025
0.25
30
2
0
0
CS
0.25
1.0
36
18
CX
0.25
1.0
36
36
HC
2U
48
Ti me ( hr )
72
100
Fig. 2. Alteration of glucose level in the lens after HC was administered to 15-day-old chick embryos (0 hr). Lenses were removed at
the indicated times after HC administration. Glucose content was
determined as described in Materials and Methods and calculated as
nmoles per lens. Data were expressed as mean ± SE (n = 4-30). In
the cases of circles without bars, the bar ranges were smaller than the
diameters. Classification of the lenses from HC-treated chick embryos;
100% at stage I at 4 and 10 hr; 30% at stage I and 70% at stage IIIII at 24 hr; 5% at stage I, 5% at stage II—III, and 90% at stage IV-V
at 48 hr; 20% at stage I, 45% at stage II—III, and 35% at stage IV-V
at 72 hr; 75% at stage I, 19% at stage II—III, and 6% at stage IV-V at
100 hr.
Glucose GSH
I
36
Control
PS
Blood
Glucose
%
100
%
100
%
100
0
32
523
2000
70
42
200
4
0
2
34
753
2270
84
39
240
0
0
0
12
0
6
10
270
98
64
93
0
0
0
0
0
0
46
65
87
78
84
117
Steroid at the indicated dosage was dissolved in 0.2 ml of sterilized water
and administered to 15-day-old chick embryos. At 48 hr after steroid administration, lenses and blood were removed. Lenses were classified to stage I to
stage V, as described previously.' Data were expressed as number of embryos.
The determination of glucose and glutathione in pooled lenses and that of
glucose in blood were carried out as described in Materials and Methods. Data
were expressed as mean % of control from three experiments for lens and as
mean % of control from 5-10 embryos. HC = hydrocortisone hemissucinate
sodium, PS = prednisolone hemisuccinate sodium, CS = cortisone hemisuccinate sodium, CX = cortexolone hemisuccinate sodium, GSH = glutathione.
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No. 1
per egg of CS showed some effects, but that of
CX did not. In the alteration of blood glucose after
glucocorticoid administration, HC and PS showed the
elevation, of glucose, but CS and CX did not. Since
cortisone and cortexolone are known to have weak or
negligible glucocorticoid activity in the developing
chick embryo as well as in mammals, 519 ' 20 cataract
formation and associated phenomena seemed to be
closely related to glucocorticoid activity.
It is known that hyperglycemia caused by sugar6"8
or by chemicals9 can induce cataracts in animals. The
marked elevation of glucose in the lens after glucocorticoid administration suggests that there are similarities
between glucocorticoid-induced cataract and sugar
cataract. To study this further, the amount of water,
sorbitol, fructose, and glycosylation of protein in control and HC-cataractous lens were determined at 48 hr
after HC-treatment (Table 4). Wet weight of control
lens and HC-cataractous lens were 6.02 ± 0.04 mg and
5.42 ± 0.1 mg, respectively. The water content in HCcataractous lens was also lower than that in control.
Sorbitol and fructose in both control and HC-cataractous lens were undetectable. The amounts of 5-hydroxymethyl-furfural released from the glucosyl moiety
in ketoamine linkage of protein were negligible in both
control and HC-induced cataractous lenses, with no
difference between them.
Thus, the data showed no correlation between the
extent of sorbitol and cataract formation, and that of
glycosylation and cataract formation.
It was also interesting to know whether the alteration
of glucose level in the lens is directly related to lens
opacification. Therefore, we determined the effect of
ascorbic acid, which is known to prevent HC-induced
cataract formation,3 on the elevation of glucose induced
Table 4. Effect of HC-treatment on fructose, sorbitol,
and protein glycosylation
%of
Control
Cataract
control
6.02 ± 0.04
4.99 ±0.04
82.9
5.42 ±0.10
4.40 ± 0.09
81.2
90.0
88.2
97.9
Fructose/20 lenses
Sorbitol/20 lenses
nil
nil
nil
nil
5-hydroxymethylfurfural/10 lenses
nilf
nil*
Wet weight (mg/lens)*
H2O content (mg/lens)
H2O/wet weight (%)
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ELEVATION OF GLUCOSE IN GLUCOCORTICOID CATARACT / Nishigori er ol.
HC (0.25 /zmole/cgg) was administered to 15-day-old chick embryos and 48
hr later their lenses were removed and assayed.
* Ten lenses from five embryos were pooled. Their wet weight and dry weight
were determined and calculated as per lens. Four more experiments were done,
and data were expressed as mean ± SE. Fructose, sorbitol, and 5-hydroxymethylfurfural were determined by the methods described in Materials and Methods. Three experiments were done.
t Below 0.4 nmole/9.5 mg protein.
$ Below 0.4 nmole/9.1 mg protein.
Fig. 3. Glucose content in
50
the lenses obtained from
control, HC-treated, and HCascorbic acid (VC)-treated,
40
chick embryo. The 15-dayold, chick embryos treated
c
with HC (0.25 ^mole/egg)
were given ascorbic acid (20
o
^moles/egg) at 3, 10, and 20
E
hr after HC administration.
c
At 48 hr after HC treatment,
in 20
the lenses were removed and
o
o
classified. Glucose content
5
was determined and calcu10
lated as nmoles per lens. Data
were expressed as mean ± SE
(n = 4). The data of HC were
obtained from stage IV-V
HC
HC+VC
lenses. The data of HC + VC
were obtained from stage I lenses. HC: I (0%), IV-V (94%). HC + VC:
I (56%), II—III (24%), IV-V (20%).
1
•
-
1
-
by HC. As shown in Figure 3, the glucose content of
stage I lenses from HC-ascorbic acid treated embryos
was lower than that of IV-V lenses from HC-treated
embryos, but was still 14-fold higher than the control
level.
Discussion
Clinically, glucocorticoids are among the most valuable drugs for treatment of numerous diseases. However, high-dose or long-term therapy with glucocorticoids is well known to cause side effects. Therefore, it
is important to clarify the mechanisms for side effects,
such as cataract formation, and to find a preventive
procedure against side effects without the loss of therapeutic activities.
The mechanism of glucocorticoid-induced cataract
formation has not been clarified, although there are
several possibilities for direct or indirect effects of glucocorticoid on the lens. As a direct effect, glucocorticoid
may produce alterations of metabolic activities in the
lens,21"23 or it may react with lens protein, such as crystallin.24"26 Recently, Manabe et al24 demonstrated that,
when rat lens was incubated with prednisolone, formation of a prednisolone-lenticular protein adduct and
cataract occurred. Bucala et al25 also showed, by injecting steroids into the vitreous chamber of the rabbit
eye, that cortisol (hydrocortisone), dexamethasone, and
prednisolone could produce cataract, but 17a-hydroprogesterone and 4-pregnen-l 1/3,17a,20«,21-tetrol-3one did not. They suggested the formation of a Schiff
base through the amine of lens protein and the C-20
carbonyl of corticoids, followed by a Heys rearrangement with the C-21 hydroxyl to produce a stable ketoamine product. However, it is unlikely in our studies
that a Schiff base formation at the C-20 carbonyl in
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INVESTIGATIVE OPHTHALMOLOGY 6 VISUAL SCIENCE / January 1987
hydrocortisone, prednisolone, and other corticoids was
involved in cataract formation. The reasons are as follows. Hydrocortisone, prednisolone, cortisone, and
cortexolone, which have in common the 17a-OH and
the 17.-0 side chain with the C-20 carbonyl and the C21 hydroxyl groups, were examined in their cataractogenic activity by using their 21-hemisuccinate sodium
forms. Hydrocortisone and prednisolone, which have
a hydroxyl group at the C-11/3, could produce cataract
and cause alterations of lens composition. However,
cortisone, which, in chick embryos, is poorly converted
to hydrocortisone by reduction at the C-l 1 ketone, 1920
could not produce cataract at the same dose as hydrocortisone and prednisolone, but it showed some effect
at 1.0 jmiol/egg. Cortexolone, without the C-l 1/3 hydroxyl in corticoid, at 0.25 and 1.0 /^mol/egg, could
not produce cataract. Since the C-l 10 hydroxyl group
in the structure of corticoid is essential for glucocorticoid activities,1920 these data demonstrate that cataractogenic activity relates to glucocorticoid activities.
Glucocorticoid-induced cataractous lenses in developing chick embryos display at least three common
phenomena in the alteration of lens components: an
elevation of glucose, a decline of glutathione,'*2 and an
elevation of lipid peroxide.27 Glucocorticoid alters
metabolic activities in several tissues, which can cause
changes in humoral components, such as elevation of
blood glucose4 and lipid peroxide.28 It is likely that
these substances invade and influence the lens, leading
to the loss of transparency. In mammals, adrenocortical
hormones have profound effects on glucose and protein
metabolism, resulting in the tendency toward hyperglycemia.4 Similar processes may be involved in the
elevation of blood glucose level after glucocorticoid
administration to developing chick embryos. Glucose
is the primary source of metabolic energy in the lens,
and is derived from blood via the ocular fluids-aqueous
and vitreous humor.29"31 In ovo, the levels of glucose
in blood and lens at 48 hr after HC administration
were calculated as mM values. In controls, the lenticular level was 0.33 ± 0.04 mM (based on wet weight;
Table 4) which was about 1/25 of the blood level. In
developing chick embryos with cataract, the concentration in lens and blood increased and became 8.73
±1.15 mM and 15.80 ± 0.73 mM, respectively. Thus,
it was found that, after HC administration, the elevation of lenticular glucose level was marked, and did
not occur parallel to that of blood glucose level.
"Glucose" level in the lens is also dependent on the
metabolism of glucose. In fact, after HC treatment, the
metabolism of glucose in the lens is altered; hexokinase
activity in HC-cataractous lens was about 80% of control (not shown), although glucose-6-phosphate content
in HC-induced cataractous lens was about 1.4-fold
above control (possibly through the elevation of "glu-
Vol. 28
cose" substrate). Therefore, it would seem that the elevation of "glucose" in the lens after HC administration
may be mainly due to the elevation of "glucose" in
blood and ocular fluids.
Concerning the mechanism of sugar-induced cataract formation, the glycosylation of lenticular protein11-32"35 and the "osmotic theory" caused by accumulation of sorbitol 1011 have been considered.
Studies on the lens protein11'32-33 from diabetic and
nondiabetic animals indicated that increased glycosylation might contribute to the development of sugar
cataract. On the contrary, there have been reports
which did not reveal significant differences in glycosylation of lysine in lens crystallins between diabetics
and non-diabetics in both animals and humans. 34 ' 35
Piatigorsky et al demonstrated that delta-crystallin from
15-day-old chick embryo lens contains lysine (33.5—
33.7 moles/50000 daltons).36 Therefore, it was interesting to know whether glycosylation of protein occured
in glucocorticoid-induced cataract in developing embryos. As shown in results, however, it was found that
glycosylation of protein was negligible in HC-induced
cataractous lens (below 0.4 nmole/9.1 mg protein), as
well as control lens (below 0.4 nmole/9.5 mg protein).
Alternatively, it has been hypothesized that, when
glucose enters the lens to form a sugar alcohol, it brings
in water and changes the ionic balance, which causes
swelling and vacuole formation, leading to cataract. 101 '
However, several studies have demonstrated that the
onset of either diabetic or galactosemic cataract occurred without affecting the accumulation of polyol,
and that diabetic cataracts may be prevented by diets
high in fat and protein37 or antioxidant, such vitamin
E,38 although there was still an elevation of polyol in
the lens to levels similar to those found in untreated
rats. In the present studies, we supposed that the synthesis and the accumulation of sorbitol in HC-cataractous lenses could occur, since "glucose" level was
markedly accumulated. It was found that vacuoles between cortical and nuclear region were formed in HCinduced cataractous lenses (not shown). However, as
demonstrated in the results, sorbitol and fructose could
not be detected in HC-induced cataractous lenses, nor
in control lenses. Furthermore, dehydration was observed in HC-induced cataractous lenses. The present
data indicate that glucocorticoid-induced cataract of
developing chick embryos could not be understood, at
least by either glycosylation of protein or the elevation
of sorbitol.
The loss of transparency occurred with the elevation
of glucose in the lens, and lens opacity disappeared
with a return to control glucose level. It was thought
possible that the high content of glucose in the lens
leads to the loss of transparency. Ross et al38 have indicated that the glucose, fructose, and sorbitol levels
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ELEVATION OF GLUCOSE IN GLUCOCORTICOID CATARACT / Nishigori er ol.
were increased to similarly high or significantly higher
levels in the noncataractous lenses of the diabetic rats
treated with vitamin E, compared with the cataract
lenses of the untreated diabetic animals. They described
that sugar cataract was not simply caused by a change
of osmolarity. We found that the levels of glucose in
stage I of noncataractous lenses from HC-ascorbic acidtreated developing chick embryos was approximately
70% of that of cataractous lenses, but was still around
14-fold above that of control lenses. It was not conceivable that the amount of glucose in the lens was a
critical factor between transparency and opacity of lens.
It was also found that the glucose in the lenses consisting of 30% of stage I and 70% of stage II—III at 24
hr after HC treatment was almost equal to that in the
lenses consisting of 5% of stage I, 5% of stage II—III,
and 90% of stage IV-V at 48 hr after HC treatment.
These results argue that glucocorticoid-induced cataract
could not be caused by osmotic change, depending on
glucose level.
Thus, glucose elevation may not be directly related
to glucocorticoid-induced cataract in developing chick
embryos. However, a role for glucose in some aspect
of the process cannot be ruled out. Our previous papers
have suggested that glucocorticoid-induced cataract
formation proceeded via a step of oxidation or peroxidation, since the cataract formation can be suppressed by radical scavengers, such as ascorbic acid,3'27
vitamin E (not shown), and N-(2-mercaptopropionyl)glycine.2 However, the mechanism of production of free radicals in ovo caused by glucocorticoid
administration remains obscure. Crabbe hypothesizes
that autooxidation of glucose producing free radicals
may be involved in sugar cataract.39 Although there
are controversial opinions against Crabbe's hypothesis, 939 his hypothesis still seems to be interesting at the
present time.
However, glucocorticoid has multiple activities in
living systems. The effects of one insult or change may
be subliminal; when several are combined, they can
have a synergistic action in initiating or potentiating a
cataractogenic effect. To clarify the mechanism of glucocorticoid-induced cataract formation, other processes
must also be considered.
Key words: cataract, chick embryo, glucocorticoid, glucose,
cortexolone
Acknowledgment
We are indebted to Dr. D. O. Toft for his advice.
References
1. Nishigori H, Lee JW, and Iwatsuru M: An animal model for
cataract research: cataract formation in developing chick embryo
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173
2. Nishigori H, Hayashi R, Lee JW, and Iwatsuru M: Effect of
MPG on glucocorticoid-induced cataract formation in developing
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3. Nishigori H, Hayashi R, Lee JW, Maruyama K, and Iwatsuru
M: Preventive effect of ascorbic acid against glucocorticoid-induced cataract formation of developing chick embryo. Exp Eye
Res 40:445, 1985.
4. Ensinck JW and Williams RH: Disorder causing hypoglycemia.
In Textbook of Endocrinology, 5th ed, Williams RH, editor.
Philadelphia, London and Toronto. WB Saunders Company,
1974, pp. 627-659.
5. Koehler DE and Moscona AA: Corticosteroid receptors in the
neural retina and other tissues of the chick embryo. Arch Biochem
Biophys 170:102, 1975.
6. Sterling RE and Day PL: Blood sugar levels and cataract in Alloxan-treated, galactose-fed and xylose-fed weanling rats. Proc
Soc Exp Biol 78:431, 1951.
7. Van Heyningen R: Formation of polyols by the lens of the rat
with "sugar" cataract. Nature (London) 184:194, 1959.
8. Patterson JW: Course of diabetes and development of cataracts
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