即効性ある男性用避妊薬、マウスで効果確認

【パリＡＦＰ＝時事】女性用の緊急避妊薬「モーニング・アフターピル」があるならば、性交渉の前に男性が必要に応じて服用する「アワー・ビフォーピル」ができる日は来るのだろうか。開発中の新薬を雄のマウスに投与したところ、１時間以内に生殖能力が低下し、ほぼ１日後に復活したとする実験結果が１４日、英科学誌ネイチャー・コミュニケーションズに発表された。（写真は資料）
　論文の共著者である米ワイル・コーネル医科大学のヨッヘン・バック氏は、精子の「スイッチをオンにする」働きを持つ酵素の可溶性アデニル酸シクラーゼに着目したと説明。この酵素が阻害されると、精子の動きが悪くなるという。
　この酵素を阻害する化合物をマウスに投与したところ、精子が３０分から１時間で一時的に不活発化した。避妊効果は投与から２時間までは１００％で、３時間後には９１％に低下した。２４時間後に生殖能力は正常に戻ったとしている。
　バック氏によれば、研究チームは、単回投与で１時間以内に作用し、６～１２時間効果が持続する非ホルモン性ピルの開発を目指している。
　男性用の避妊薬については現在、ジェル状のホルモン剤などのヒト臨床試験が進められているが、いずれも、効果を発揮し、再び精子が正常化するまでにそれぞれ数週間から数か月を要する。
　また、これまでの研究では、可溶性アデニル酸シクラーゼが慢性的に阻害され、生殖能力のない男性は、腎臓結石の罹患（りかん）率が高いとされてきた。
　しかし、バック氏は、今回の研究ではマウスに副作用は見られなかったと説明。結石ができるのは酵素が阻害される状態が慢性化しているのが原因で、この避妊薬ではそうした問題は起きないないはずだと述べた。
　さらに、３年以内にヒト臨床試験を開始したいとして、製品化までに８年はかかるとの見通しを示した。
　研究に参加していない英アングリア・ラスキン大学の避妊法の専門家スーザン・ウォーカー氏は、製品化を疑問視する一方で、即効性があるという利点は「性交渉の相手のピル服用を確認する機会」につながると評価した。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2023/02/17-16:42）

If women have the morning after pill, could men one day have an hour before pill?
A new drug candidate renders male mice infertile within an hour and wears off in less than a day, an experimental study said Tuesday, potentially pointing towards a future on-demand male contraceptive.
The potential drug, which has not been tested in humans and remains years away from possibly becoming available, joins a growing number of male contraceptives in development.
However there are currently only two options available for men: condoms and vasectomies.
Previous drugs have struggled partly because the bar for side effects is believed to be far higher for men -- because they do not risk getting pregnant -- as well as a lack of interest from the pharmaceutical industry.
For women, right now all the burden of contraception is on us, Melanie Balbach, a pharmacology researcher at Weill Cornell Medicine in the US, told AFP.
We want new options, said Balbach, the lead author of the study published in Nature Communications.
The team of researchers targeted an enzyme called soluble adenylyl cyclase, which acts as the on switch for sperm, said study co-author Jochen Buck, also of Weill Cornell Medicine.
If the enzyme is switched off, the sperm can no longer move, he said.
Across several different tests, the researchers showed that a compound which blocks the enzyme renders mice sperm immobile in 30 minutes to an hour.
The compound was 100 percent effective in preventing pregnancy within the first two hours, dropping to 91 percent in the first three hours, the study said.
After 24 hours, the mice sperm moved like normal again.
- 'Eye-catching advantage' -
The researchers hope are aiming for a single non-hormonal pill that works in under an hour and lasts six to 12 hours, Buck said.
This would be much different to other options under development, such as a hormonal gel currently going through human trials, which all take weeks or months to start and stop working.
No side effects were noticed in the mice. Previous research has suggested that infertile men who had their soluble adenylyl cyclase enzyme permanently switched off had an increased rate of kidney stones.
Buck said this was the result of their enzyme always being off -- which would not be the case for men taking an on demand pill.
The researchers hope to hold the first trials on humans within three years, with a final product possibly up to eight years away, Buck said.
Susan Walker, an expert in contraception at the UK's Anglia Ruskin University not involved in the research, said she was a little sceptical a pill would actually make it to market as so many other efforts have fallen short.
But the eye-catching advantage of almost immediate effectiveness offered the possibility of seeing a sexual partner take a pill, she said.
The consultancy Desire Line is working on forecasting the potential uptake of a range of male contraceptive products, according to its founder Steve Kretschmer.
Initial estimates indicate in the United States that uptake for an on-demand pill which has quick onset of action and 1-2 days duration of action could be about triple that of Viagra when it was initially launched, he told AFP.