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The effects of glucose on chick embryonic development

Kristin Parish, Jessie Brown, Renee Cook, Megan Kapp

• A mother having diabetes PRIOR to

pregnancy (Type I or Type II)

• A mother developing diabetes

DURING pregnancy (Gestational

Diabetes)

Two Types of Problems:

Gestational Diabetes

• Pregnant women who have never had diabetes

before but who have high blood glucose levels (Occurs later in pregnancy)

• Affects 18% of pregnancies world wide, approximately 10% of pregnancies in the U.S.

Causes of Gestational Diabetes

Hypothesis so far: 1. Hormones from the placenta that help the baby

grow and develop may block the action of the mothers insulin in her body. (INSULIN RESISTANCE)

This makes it harder for the mother’s body to use insulin and requires a higher concentration of insulin to be effective.

http://www.pre-diabetes.com/download/medical/how-insulin-works.jpg

Diabetes & Development

• The risk of major malformations is markedly increased in infants of diabetic mothers, ranging from 4% to 10%

• This is two to three fold higher than the general population!!

Effects of Gestational Diabetes

Without enough insulin, glucose cannot leave the blood and be changed to energy.

The buildup of glucose is called hyperglycemia Undiagnosed gestational diabetes can hurt the developing fetus by having excess blood glucose cross the placenta Babys pancreas must make extra insulin to get rid of glucose

Glucose is stored as fat, resulting in macrosomia

http://www.healthcentral.com/common/images/1/19724_10459_5.jpg

Developmental defects

Areas most common for pre-existing diabetes: - cardiovascular system - central nervous system -facial and limb development

Developmental Defects

Specific abnormalities associated with gestational diabetes: • Musculoskeletal (20/1000 births)

-Caudal regression -Limb reduction -Club foot

• CNS (5/1000 births) - Exencephaly & encephaly - Spina bifida

• Cardiovascular (34/1000 births)

- Ventricular septal defect - Transposition of vessels - Single ventricle

Important developmental stages in chicks:

~ 20 hours after incubation: - CNS development - Eye development - Heart development

~ 72 hours after incubation: -Limb development -Beak development

http://chickscope.beckman.uiuc.edu/resources/egg_to_chick/figures/figure10.jpg

Glucose in excessive amounts will demonstrate itself as a teratogen. Embryos administered glucose at ~21 hours in development will acquire more developmental defects, or a higher mortality rate, than those administered glucose at ~72 hours of development

Hypothesis

Experimental Methods

• Twelve in-vivo chick cultures were used to isolate the effects of glucose on the developing embryo

• Glucose concentrations were tested at 75 mM/ L and 125 mM/L

• Two different developmental time periods were tested : ~21 hours after incubation, and ~72 hours after incubation

Experimental Methods FIRST WEEK: ~ 21 hours after initial incubation (4) Control cultures – chicken saline ONLY (4) 75 mM/L cultures – glucose and chicken saline solution (4) 125 mM/L cultures – glucose and chicken saline solution 5

* 50 uL additions of solution were injected into egg yolk approximately 2 cm from blastodisc

Experimental Methods SECOND WEEK: ~ 72 hours after initial incubation (4) Control cultures – chicken saline ONLY (4) 75 mM/L cultures – glucose and chicken saline solution (4) 125 mM/L cultures – glucose and chicken saline solution 5

* 50 uL additions of solution were dripped onto blastodiscs, and eggs were placed back into the incubator

Experimental Methods

• Initial observation while embryo was still in shell, further observations made by emptying shell into dish

• Observations were made after a total of 6 days of incubation

• ~21 hour glucose addition were observed 5 days later • ~72 hour glucose addition were observed 3 days later

Results

25% of eggs developed in the presence of glucose

75% of eggs displayed minimal vascularization and did not develop past initial vascularization

100% of eggs did NOT develop past initial vascularization in presence of glucose

Control: 50% of eggs displayed vascularization, but no development. 50% showed no signs of fertilization or development

Results 125 mM glucose treatment ~ 21 hours

Culture #2 Culture # 3

75 mM glucose treatment ~21 hours

Culture #2 Culture #2

Results

Whats affected?

Primary Neurulation - Closure of the neural tube, specifically- the anterior

neuropore resulting in exencephaly and encephaly, spina bifida

Possible that excessive glucose interferes with folate absorption

http://img.medscape.com/fullsize/migrated/470/598/nf470598.fig6.gif

What’s affected?

Neural Crest Cells - Cardiac Neural Crest * Failure to produce proper septum tissue - Cranial Neural Crest * Facial development abnormalities Lateral Plate Mesoderm -Further development of the heart -Limb development

Chick embryos under development of excessive glucose. C- macrosomia D- abnormal tension and flexion in spine

Discussion

Overall, excessive glucose = BAD for development

- Excessive glucose is more detrimental and more likely to lead to

termination of pregnancy if available prior to beginning of development of the heart and nervous system (21 hours into development)

- Excessive glucose provided after beginning of development of heart and nervous system will have a less lethal effect, however will exhibit malformation in development.

References Datar, S, Bhonde, R. 2006. Shell-less Chick Embryo Culture as an Alternative in vitro Model to Investigate Glucose-Induced Malformation is Mammalian Embryos. Rev Diabetes Study. 4:221-227 Dietz, W. C 1994. Critical periods in childhood for the development of obesity. Journal of Clinical Nutrition. 59:955-959 Hughes, A, Fadem, F. 1974. The Teratogenic effects of sugars on the chick embryo. Journal of Embryology. 32:661-674 Karlsson K, Kjellmer I. 1972. The outcome of diabetic pregnancies in relation to the mother’s blood sugar level. Am J Obstet Gynecol. 112:213–230