Embryo Metabolism

Question 1

Contrast between biosynthetic activity in an embryo pre-compaction and post-compaction.

Answer 1

Low vs. high, respectively.

Question 2

Contrast between QO2 in an embryo pre-compaction and post-compaction.

Answer 2

Low vs. high, respectively.

Question 3

Contrast between preferred nutrient in an embryo pre-compaction and post-compaction.

Answer 3

Pyruvate vs. glucose, respectively.

Question 4

Contrast between preferred amino acids in an embryo pre-compaction and post-compaction.

Answer 4

Non-essential vs. both essential and non-essential, respectively.

Question 5

Contrast between genomes in an embryo pre-compaction and post-compaction.

Answer 5

Maternal vs. embryonic, respectively.

Question 6

What (non-essential) amino acids are needed pre-compaction?

Answer 6

Alanine, Aspartate, Asparagine, Glutamate, Glutamine, Glycine, Proline, Serine, Taurine.

Question 7

What are seven functions of amino acids in an early developing embryo?

Answer 7

1. Biosynthetic precursors
2. Regulators of energy metabolism
3. Osmolytes
4. Buffers of intracellular pH
5. Antioxidants
6. Chelators

Question 8

What two major pathways do early embryos use to generate energy?

Answer 8

Glycolysis and tricarboxylic acid (TCA) cycle.

Question 9

How do cumulus cells surrounding the early embryo pre-compaction aid in embryo metabolism?

Answer 9

The cells break down glucose into pyruvate and lactate for the embryo to further break down for energy.

Question 10

Blastocysts need a high concentration of what in the uterine environment for energy?

Answer 10

Glucose.

Question 11

When is glucose required by an embryo and why?

Answer 11

Before implantation; as precursors to triacylglycerides, phospholipids, mucopolysaccharides and glycoproteins (and obviously as energy to fuel DNA synthesis etc. etc.).

Question 12

For what two reasons is NADPH required by a growing embryo?

Answer 12

1. Synthesis of lipids and other complex molecules.

2. Reduction of cellular glutathione (an antioxidant for embryos).

Question 13

What is the enzyme used in the reduction of pyruvate to lactate during embryo cleavage?

Answer 13

Lactate dehydrogenase

Question 14

Reduction of pyruvate to lactate in cleavage-stage embryos makes what as a byproduct and what is it used for?

Answer 14

NAD+ used for anaerobic metabolic conditions.

Question 15

Where is the pyruvate from which a cleavage-stage embryo gets its nutrition present?

Answer 15

Follicular & reproductive tract fluid.

Question 16

What is the difference between pyruvate uptake by in vivo vs. in vitro babies?

Answer 16

In vivo = more uptake.

Question 17

Between pyruvate, lactate, and amino acid uptake, which may provide the most reliable information on embryo viability?

Answer 17

Amino acid uptake.

Question 18

A developmentally competent embryo is associated with what kind of amino acid “turnover”?

Answer 18

Low.

Question 19

What is the major amino acid depleted from culture medium of embryos in vitro?

Answer 19

Leucine

Question 20

What are four methods of analyzing embryo metabolism in vitro?

Answer 20

1. Altering culture medium (i.e. glucose vs. pyruvate, etc.)
2. Comparing uptake of metabolites (non-invasively).
3. Using radioactive precursors and measuring products.
4. Using metabolic inhibitors which can be phosphorylated but not metabolized, for example.

Question 21

Explain how to non-invasively assess embryo uptake of metabolites.

Answer 21

1. Serial nanoliter samples taken with glass capillary tube.
2. Analyzed for carbohydrates, amino acids, ammonium, oxygen, and enzymes.
3. Note: Nanoliter pipette has special design with mineral oil, air, wax, metal holding tube, and rubber tubing attached to syringe.

Question 22

How can a spectrophotometer (or fluorescent microscope) be used to non-invasively assess embryo uptake and utilization of nutrients?

Answer 22

1. Machine records changes in light absorption over time.

2. Changes are plotted against a standard curve for estimation purposes.

Question 23

Compare the partial pressure of oxygen between oviductal environment and venous blood.

Answer 23

Oviductal environment has lower partial pressure of oxygen.

Question 24

What would a low level of acidity in an early embryo indicate about its metabolism and, thus, viability?

Answer 24

Low metabolism and low viability.

Question 25

Is pyruvate uptake a better indicator of embryo viability than morphology and why?

Answer 25

No; studies show that human embryo pyruvate uptake levels vary pretty widely and there is a generous range for which embryos can be considered viable (10 to 30pmol/embryo/hr on day 2).

Question 26

When GLUT1 was inhibited in developing embryos, what happened to the blastocysts (and what adult medical condition does it have implications for)?

Answer 26

Increased blastocyst apoptosis (somehow this relates to diabetes).

Question 27

Why is glucose uptake a poor indicator of embryo metabolism/quality?

Answer 27

Because somehow according to the lecture, embryos need oxidative phosphorylation for 72% of their energy but they still convert glucose into lactate instead (doesn’t make sense but ok…).

Question 28

Why might high levels of glucose harm embryos?

Answer 28

Inhibits oxidative phosphorylation in many cell types like tumors and yeast (called “Crabtree effect”).

Question 29

Explain the “Crabtree effect.”

Answer 29

In high glucose conditions, some cells take steps to preserve oxygen by avoiding the citric acid cycle and instead continue glycolysis despite the inadequate energy production which winds up impairing embryo growth.

Question 30

What are three things to consider in the argument to use or not to use glucose in in vitro embryo medium?

Answer 30

1. Studies show no glucose = better quality embryos (but, no difference in pregnancy rates).
2. Glucose is not only present in female reproductive tract, but embryos possess mechanisms to allow glucose entry into cells.
3. Therefore, not allowing glucose in vitro is something unnatural and introduced by IVF (according to slides).

Question 31

What are two things to consider in regards to using EDTA and amino acids in in vitro embryo culture medium?

Answer 31

1. Both EDTA and amino acids independently inhibit glycolysis and increase oxidation in embryos.
2. Both specifically work together to do this during the cleavage-stage embryo, which results in improved embryo quality.

Question 32

What is the co-culture technique for embryo medium?

Answer 32

Embryos are cultured on monolayer of endometrium or cumulus cells.

Question 33

What is one pro/con of co-culture for embryo medium?

Answer 33

1. It aims at mimicking biological conditions (pro).

2. It’s expensive and difficult to replicate (con).

Question 34

Why is co-culture for embryo medium believed to improve existing culture conditions?

Answer 34

Releasing growth factors or metabolites and eliminating toxins or both.