L15: Male Contraception

Question 1

where is sperm generated and what is the pathway of sperm?

Answer 1

• Sperm is generated from reproductive cells in the seminiferous tubules of the testis.
• Pathway:
  1. testis
  2. epididymis
  3. Vas deferens
  4. Urethra for ejaculation

Question 2

What is the epididymis?

Answer 2

A single long tube where sperm acquires the ability to fertilize an oocyte (the sperm matures in the epididymis).

Question 3

What is spermatogenesis? How long does it take in humans?

Answer 3

The process where the diploid stem cells (spermatogonia) become haploid spermatozoa after a round of mitosis and meiosis 1 and 2, and differentiation to acquire the ability to swim. In humans this takes 64 days.

Question 4

Why is male contraceptives so challenging?

Answer 4

Because females release one oocyte per month, while males produce lots of sperm at every heartbeat, so it is much more difficult to regulate and stop this production.

Question 5

Describe the hormone regulation of the testis.

Answer 5

1. Hypothalamus releases GnRH
2. GnRH stimulates the gonadotrophs in the anterior pituitary gland which triggers the release of LH and FSH.
3. LH and FSH act on the cells of the testis.
   Each step is under the regulation of transcription factors and chemicals.

Question 6

What cells do LH and FSH act on? Why?

Answer 6

They act on:
1. Sertoli cells (acted on by FSH)
2. Leydig cells (acted on by LH)
Why? because spermatozoa lack LH and FSH receptors.

Question 7

Where are leydig cells found? What do they do?

Answer 7

Leydig cells are found outside of the seminiferous tubules in the interstitial space.
What do they do:
1) LH acts on the LH receptors of leydig cells which triggers the synthesis of testosterone in these cells.
2a) The testosterone is released into the blood and causes feedback inhibition of LH and GnRH.
2b) Testosterone is also transported to sertoli cells.
3. The testosterone released has both a local effect on the seminiferous tubules as well as on other cells that it reaches as it is released into the circulation.
The concentration of testosterone is 10x higher in the seminiferous tubules than in the circulation.

Question 8

What cells are found inside the seminiferous tubules?

Answer 8

1. Sertoli cells

2. Germ cells

Question 9

Where are sertoli cells found? What do they do?

Answer 9

Found inside the seminiferous tubules. FSH acts on sertoli cells. They are the nurse/mother cells of germ cells because the germ cells are embedded inside of them. High local testosterone is necessary for the maturation of sperm cells into spermatozoa.

Question 10

Where and how is testosterone made in males?

Answer 10

Testosterone biosynthesis occurs in leydig cells, driven by LH. You need high pools of cholesterol. Cholesterol side chain is cleaved by an enzyme to make pregnenolone. Pregnenolone can be further modified into testosterone. Testosterone can be further metabolized into dihydrotestosterone (DHT) and estradiol (E2).

Question 11

How is DHT made from testosterone? What is the structural difference? What can it do?

Answer 11

Testosterone is converted into dihydrotestosterone (DHT) by the enzyme 5-alpha reductase (1 and 2). The modification is the reduction of a double bond on testosterone. DHT can interact with Androgen receptors like testosterone but it has a higher Affinity to them than testosterone.

Question 12

How is E2 made from testosterone? What is the structural difference? What can it do?

Answer 12

Testosterone is converted to estradiol (E2) by the aromatase enzyme and the structural difference is that it makes an aromatic ring. Estradiol is necessary for the production of estrogen in the testis. Testosterone and estradiol provide negative feedback to the hypothalamus and to the anterior pituitary gland to inhibit synthesis of GnRH, LH, and FSH

Question 13

On what chromosome is the human androgen receptor found?

Answer 13

The X chromosome.

Question 14

What are the domains for the human androgen receptor (AR)? What hormones bind to it? What does it do?

Answer 14

• Domains: Ligand binding domain and DNA binding domain.
• It is homologous to the nuclear estrogen and progesterone receptors.
• The ligand binding domain (LBD) is bound by testosterone and dihydrotestosterone (DHT).
• The receptor is highly sensitive to DHT so its binding causes more activity.
• The receptor dimerizes upon ligand binding and interacts with androgen response elements in the genome to turn on the synthesis of genes that are androgen dependent.

Question 15

What does the presence of 5-alpha reductase or aromatase enzyme in local tissues allow?

Answer 15

The presence of 2 different enzymes allows for the differential expression of the enzymes across tissues. This means that in some tissues, unmodified testosterone will act, and in others, it will be converted to DHT, and in some to estradiol.

Question 16

What is the steroid pyramid?

Answer 16

Cholesterol is found in the highest concentrations and steroids are found in the lowest. Cholesterol>progestins>androgens>estrogens. Although there is a low concentration of estrogens, it is sufficient to influence the body.

Question 17

What are the major sites of action of testosterone? What does it do there?

Answer 17

1. Mainly muscle, bone marrow, bone, and brain.
2. Skin: hair growth, balding, sebum production.
3. Muscle: increase in strength and volume.
4. Liver: synthesis of serum proteins (ex: athletes using androgen often have liver problems).
5. Kidney: stimulation of erythropoietin.
6. Bone marrow: stimulation of stem cells.
7. Bone: accelerated linear growth, closure of epiphysis (ex: men are usually taller than women due to androgen induced growth).
8. Brain: libido and aggression.
9. Male sexual organs: penile growth, spermatogenesis, epididymal sperm maturation, prostate growth and function.

Question 18

What are the major sites of action of DHT?

Answer 18

External genitalia, prostate, skin, and hair.

Question 19

What are the major sites of action of estradiol?

Answer 19

Bone, brain, breasts.

Question 20

Are there any approved male hormonal contraceptives?

Answer 20

NO bitch.

Question 21

What are the male contraceptive options that are currently approved?

Answer 21

1. Condoms
2. Vasectomy
3. Withdrawal

Question 22

What would be the most direct way to block sperm form being ejaculated?

Answer 22

Blocking the vas deferens.

Question 23

What were the different methods that were tried to block the vas deferens? were they successful?

Answer 23

1. Vasectomy: successful but not always reversible (vasovasotomy).
2. Injections: inject ethanol to kill the tissues in the vas deferens. Unsuccessful.
3. Implants: implants inserted in the vas deferens and allows the flow of sperm, when desired, by turning a knob. Not successful.

Question 24

What’s the purpose of hormonal contraception in males? How do they want to achieve this?

Answer 24

To regulate spermatogenesis by controlling testosterone levels.
They want to do this by regulating the amount of local testosterone that can go into the seminiferous tubules and allow for sperm maturation. This is because the testosterone present in the circulation is not enough for maturation.

Question 25

What are the hormonal approaches at regulating spermatogenesis?

Answer 25

1. Administer testosterone alone
2. Administer testosterone and estradiol
3. Administer androgen analog

Question 26

Describe what the administration of testosterone alone does. What are the challenges?

Answer 26

Although testosterone is required for spermatogenesis, administering exogenous testosterone leads to a negative feedback loop, inhibiting local testosterone synthesis. The concentration of testosterone required for spermatogenesis from the leydig cells to the sertoli cells is 10 times higher than the concentration required to maintain male features in other tissues. Therefore, in administering testosterone, it is important to find the right dose in order to enable feedback inhibition without inducing spermatogenesis. This makes it hard to find the correct dosage.

Question 27

Explain the experiment done in rabbits when administering testosterone for 3 months. What is the final conclusion.

Answer 27

Implants are given to rabbits in different concentrations and plasma testosterone is measured.

Results in circulation:

1. When no implant is in place there is a normal amount of testosterone in plasma. At intermediate doses of testosterone, the measured plasma level stays the same because the leydig cells (being slightly inhibited) are still giving most of their testosterone to the sertoli cells and therefore less to the circulation. Therefore the measured circulation is the small leydig cell contribution + implant contribution.
2. After a certain higher concentration of testosterone, the leydig cells are completely inhibited, causing a major increase in circulating plasma testosterone all coming from the implant.

Results on spermatogenesis:

1. There is a very narrow window of testosterone implant dose that completely inhibits the leydig cell’s production of testosterone.
2. On the left of the perfect dose, the leydig cells are still ON and the plasma concentration of testosterone is from the leydig cells and the capsule. Spermatogenesis is occuring.
3. On the right of the perfefct dose, leydig cells are OFF, but the dose of the capsule is so high that there is enough local testosterone from the capsule to cause spermatogenesis.

Final conclusion: too hard to predict the perfect dose. It is not reliable.

Question 28

Describe what the administration of testosterone and estradiol does. What are the challenges?

Answer 28

PDS implants, which are a combination of testosterone and estradiol, can completely shut off spermatogenesis in rats by feedback inhibition. Estradiol is much more potent in inhibiting sperm production by activating the negative feedback loop.

The balance between testosterone and estradiol dose is hard to achieve but it shows promising results. This is because serum LH was so low it became undetectable and the number of spermatozoa are much lower compared to the control while keeping serum testosterone and serum estradiol concentrations unchanged even though they were in the capsule. This is promising because the serum hormone levels are important for other bodily functions.

Challenge: hard to calibrate. Also, it takes very long to wipe out spermatogenesis.

Question 29

Describe what the administration of androgen analogs does. What are the 2 analogs?

Answer 29

1. Dimethandrolone undecanoate:
   - androgen and progesterone receptor agonist
   - Not aromatized, therefore has no estrogenic activity.
   - Not a substrate for 5alpha-redutase, so it’s not converted to DHT.
   - Allows to reduce the side effects seen in previous combination therapies (ex: estrogen)
2. 11-beta-MNTDC
   - It suppresses serum gonadotropins that would drive leydig cells to make testosterone to support spermatogenesis in sertoli cells.

1&2 could be administered as implants or pills.

Question 30

What is the main effect of non-hormonal contraception approaches in males?

Answer 30

Azoospermia (no sperm production).

Question 31

Why don’t we use cancer drugs to achieve azoospermia?

Answer 31

Cancer drugs block cell proliferation but no one wants to take drugs that are non-specifically prevent cell division. It is not targeted at meiosis which would be better.

Question 32

Why is control of retinoic acid a possible method of contraception in males?
What is a challenge?

Answer 32

Meiosis can be controlled by controlling retinoic acid. If retinoic acid is absent, no spermatogenesis will occur, so if you remove retinoic acid either from the diet or chemically at certain stages of sperm development, you can block spermatogenesis = no germ cell production.

A challenge would be to specifically block retinoic acid production in the testis because retinoic acid is needed in other tissues in the body.

Therefore an active area of research is how to block enzymes that synthesize retinoic acid in the testis.
Ex: blockage of ALDH1A enzyme by WIN 18,466 in the testis and in the liver decreases retinoic acid synthesis.

Question 33

Why is the use of Gossypol not a good male contraceptive?

Answer 33

Gossypol is a cotton seed oil extract that suppresses sperm production. It’s developed in China. It’s a daily pill. Reversibility depends on the length of exposure, was irreversible in some men, and hypokalemic effect (affected potassium levels in the body).

Question 34

Why is changing DNA packing a possible method of contraception in males?

Answer 34

DNA is 6 times more compacted in sperm than in somatic cells, this is probably a protective mechanism. The 3D architecture of DNA is different between sperm and somatic cells, therefore altering the 3D architecture would alter the capacity of sperm to swim effectively. A research possibility would be to find a drug that targets the DNA compacting specifically found in the germ cells in order to impair their swimming.

Question 35

Why is inhibiting the function of the epididymis a possible method of contraception in males?

Answer 35

The epididymis is important in the maturation of spermatozoa. When sperm leaves the testes, it is incapable of fertilizing an oocyte and must mature first in the epididymis. It takes two months for the germ cell to become a sperm. It takes 7 to 10 days for the sperm to go through the epididymis to acquire fertilization ability. Therefore, inhibiting the fertilizing ability of sperm would be an efficient male contraceptive.

Question 36

Why is immunocontraception a possible method of contraception in males?

Answer 36

There’s a blood-testis barrier in the testes to protect it from many chemicals trying to get into the testes (similar to the blood-brain barrier). You can use immunocontraception against sperm proteins and epididymal proteins; this means you develop antibodies against these proteins so that they get destroyed. A challenge of this is that it’s not very reversible. You may also use antibodies against the Germ cells themselves, but again, this method is not reversible.

Question 37

Describe the serum testosterone levels during a lifespan. When does testosterone peak? What is it useful for in this stage?

Answer 37

During puberty and adulthood there are pulsatile changes in concentrations which is linked to the temporary aggressiveness seen in adolescents.

Peaks:

1. During fetal development: important for male patterning and development of specific processes and tissues.
2. Peak in neonatal period: to modify sex specific features.
3. Puberty: spikes high and is maintained through adulthood.

Question 38

When are testosterone levels low or decreasing?

What are the consequences?

Answer 38

1. Low testosterone in pre-pubescent males.
2. Testosterone concentration and free testosterone GRADUALLY decreases over the age of 30.
   Consequences in libido, muscles, activity, etc.

Question 39

What drugs do males believe can be used to make them more youthful?

Answer 39

1. Testosterone
2. DHEA (testosterone analog)
3. Melatonin
4. Human growth hormone

This won’t make them more youthful.. Testosterone should only be used if you have an androgen deficiency (when prescribed).

Question 40

What are the methods of administration for testosterone to treat androgen deficiency?

Answer 40

1. Injection
2. Patch
3. Solution
4. Roll-on

Question 41

What are the potential benefits for hormonal replacement therapy in older men?

Answer 41

1. Preserve and improve bone mass
2. Increase muscle mass and strength
3. Increase physical functions
4. Increase libido
5. Improve well-being and mood
6. Possibly improve aspects of cognition

Question 42

What are the potential risks for hormonal replacement therapy in older men?

Answer 42

1. Headaches.
2. Baldness.
3. Strokes and blood clots.
4. High blood pressure and heart disease.
5. Impotence.
6. Aching joints.
7. Aggressive behaviour.
8. Increased risk of tendon injuries.
9. Mood swings.
10. Severe acne on face and back.
11. Development of breasts.
12. Liver damage.
13. Urinary and bowel problems.
14. Enlarged prostate.
15. Shrinking of the testicles.
16. Nausea.
17. Bloating.
18. Reduced sperm count.

Question 43

What can happen to athletes who use androgen replacement therapy to increase bone mass and growth?

Answer 43

They can become sterile.