Immunosuppressant drugs like Cyclosporine A and Tacrolimus prevent the production of an enzyme called calcineurin. This type of enzyme gives the immune system's T cells the ability to target a foreign organ in transplant patients.

Japanese scientists found a specific type of calcineurin limited to the male sperm. This type of calcineurin has two proteins - PPP3CC and PPP3R2.

The research team inhibited a lab mouse's ability to produce the two proteins. Two lab mice groups were used in the study: a 'knockout' team consisted of genetically engineered male mice unable to produce PPP3CC and PPP3R2, and a control group.

The researchers tested the hypothesis by mating the two mice group with female mice using in vitro fertilization. The 'knockout' team's sperm count was low although this does not mean they were rendered infertile. The results indicated that the 'knockout' team's sperm were unable to permeate the female egg's innermost membrane called zona pellucida (ZP).

The team performed further analysis on the 'knockout' sperms and discovered that their tails do not have the same 'whipping' rate as the regular sperms. This lowered the 'knockout' sperm's ability for egg penetration. There were also differences in the structure. The 'knockout' sperms had rigid shapes, which affected their flexibility to slip through the egg's innermost membrane.

To further test their hypothesis, the researchers injected the control group lab mice with the immunosuppressant drug. They became infertile in five days. They became fertile again after a week of no drug use.

"It is important that we find an effective and reversible contraceptive option to allow men more control over their own reproductive futures. The findings of this study may be a key step to giving men that control," said researcher Masahito Ikawa, from Osaka University.

Biomedical research director Patricia Morris from Population Control, a nonprofit research organization based in New York, commended that targeting calcineurin for potential male contraceptive pill is interesting. Calcineurin is not a hormone. Hormone-altering contraceptives would be less desirable as they can affect sex drive. Morris was not involved in the Japanese research.

The Japanese researchers expressed that they do not recommend consumers to use the two mentioned drugs as male contraceptives. The study findings aim to benefit scientists in producing a new drug. More studies need to be done in order to come up with a male contraceptive that would prevent pregnancy by targeting the two specific proteins.

The Japanese study was published in the journal Science on Oct. 1.

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