Heating the testicles could solve a major male contraceptive problem
women have one There are a variety of birth control methods, but only two methods are commonly available to men: condoms and vasectomies. Both methods have their disadvantages.
Condoms can break, and some men are allergic to latex in standard condoms. Vasectomies are surgical procedures that are painful and difficult to reverse.
So, the search for alternative male birth control options continues, and one method currently being studied is nanocontraception.
An on/off switch
Nanocontraception is based on the idea that nanoparticles — here, about 100 nanometers in diameter, or roughly one-thousandth the width of a sheet of paper or a strand of human hair — can somehow be transported to the testicles, where they can be heated.
If you could warm the testicles just a little, you would have a way to turn sperm production on and off at will, because the warmer they get, the less fertile they become. But it’s a delicate process because the testicles can be irreversibly destroyed if they get too warm; the tissue dies and can no longer produce sperm, even after the testicles return to their normal temperature.
The use of nanotechnology to heat testicles was first studied in mice in 2013 by biologist Fei Sun and his multidisciplinary research team. His early experiments consisted of injecting nanoparticles directly into mouse testicles. These nanoparticles were long nanorods (or nanocylinders) of gold atoms – imagine a tube 120 gold atoms long and 30 gold atoms in diameter – coated on their surface with some long polymer chains. They looked like elongated bacteria with sticking hairs.
The testicles of the mice were then treated with infrared radiation. As a result, the nanoparticles heated up from around 30 degrees Celsius to 37 to 45 degrees Celsius. The exact temperature depended on both the concentration of the injected nanoparticles and the intensity of the radiation.
The radiation caused heat lesions on the skin surrounding the mice’s testicles, so the procedure was thought to be painful for the animals, although there was no reliable way to measure their pain. The researchers decided to look for other ways to inject the nanoparticles.
In July 2021, Sun’s team published a paper about their latest findings. The new process’ nanorods are made of magnetic iron oxide instead of gold, and are coated with citric acid instead of ethylene glycol — but they’re the same size and shape as previous nanorods.
These magnetic nanoparticles were injected into the veins of mice and the animals were then anesthetized. A magnet was then placed next to her testicles for four hours and the nanoparticles were drawn there.
This procedure – injection followed by magnetic targeting – was performed daily for one to four days.
After the last day of treatment, an electrical coil was wrapped around the testicles, through which a current was passed. This induced a magnetic field that heated the nanorods and thus the testicles. Similar increases in temperature – from a baseline of 29 degrees Celsius (84 degrees Fahrenheit) to between 37 and 42 degrees Celsius (99 to 108 degrees Fahrenheit) – have been observed using this method. The more days a mouse was injected with nanorods, the hotter its testicles got.
Hotter testicles caused their atrophy and shrinkage, but they showed gradual recovery both 30 and 60 days after treatment as long as testicular temperatures did not reach 45 degrees Celsius (115 degrees Fahrenheit). Fertility had declined seven days after treatment—in some cases fertility had been eliminated entirely—but there was also evidence of a gradual (though not complete) recovery after 60 days.
Although fertility had not returned to normal levels, there was no appreciable difference in the litter size of the females inseminated by the treated mice, and no morphological defects were observed in any of the mouse pups. There seemed to be no difference in the sperm that came through.
And Sun and his colleagues found that, unlike the gold nanorods, which remained in mouse testes indefinitely, the iron nanorods gradually cleared into the liver and spleen and later completely out of the body. This reduced the risk of long-term toxicity.
The expense and irreversibility of surgical castration prompts many pet owners to seek alternative birth control methods. Nanocontraception is ready for use in pets, Sun says, adding that the method is already being used in cats in China.
Surgical castration is less popular in Europe than in North America, so nanocontraception may be of more interest there, says David Powell, director of the Association of Zoos and Aquariums’ Reproductive Management Center in St. Louis, Mo.
“There really isn’t a big market for pet contraceptives in the United States,” says Powell.
He adds that contraceptives aren’t typically used on livestock like sheep and cows. “They’re raised for consumption and slaughter, so the agribusiness doesn’t do much, if any, research into animal contraception.”
“Zoos are a very small market, so drug companies don’t have much motivation to make animal contraceptives,” says Powell. But some of them do, and the Reproductive Management Center is collecting data to evaluate how contraceptives work in different species.
Nanocontraception could one day be part of zoos’ reproductive toolboxes. But before that happens, more studies need to clarify how painful it is and what species the iron nanorods can be used on, Powell says. Research has shown that some mammals – such as rhinos, lemurs and dolphins – may accumulate iron, which can be toxic in larger amounts.
A potential advantage of nanocontraception is its reversibility, as zoos often attempt to accurately plan breeding events over the animals’ life cycle. But how reversible it is needs further investigation. All of Sun’s experiments treated mice only once; They were never given a second injection of nanoparticles after their testicles healed.
Sun’s ultimate goal is human contraception, although he admits there’s still a long way to go. As with zoo animals, detailed studies are needed to establish that nanocontraception is not toxic to males. It’s also more difficult to stun a man for four hours and wrap an electrical coil around his testicles than doing the same thing on a mouse. Instead, Sun hopes to deliver the magnetic nanorods orally and find another way to direct them to the testicles.
And it’s uncertain how many men will be happy with shrunken testicles, even if they return to their original size over time.
Until then, better get out the condoms.
This article was originally published on The conversation through Jeffrey Mo of the University of Toronto. Read the original article here.